Quick links: Flags Verbs Functions Glossary Release docs

DSL output statements

You can output variable-values or expressions in five ways:

Assign them to stream-record fields. For example, $cumulative_sum = @sum. For another example, $nr = NR adds a field named nr to each output record, containing the value of the built-in variable NR as of when that record was ingested.
Use the print or eprint keywords which immediately print an expression directly to standard output or standard error, respectively. Note that dump, edump, print, and eprint don't output records which participate in then-chaining; rather, they're just immediate prints to stdout/stderr. The printn and eprintn keywords are the same except that they don't print final newlines. Additionally, you can print to a specified file instead of stdout/stderr.
Use the dump or edump keywords, which immediately print all out-of-stream variables as a JSON data structure to the standard output or standard error (respectively).
Use tee which formats the current stream record (not just an arbitrary string as with print) to a specific file.
Use emit1/emit/emitp/emitf to send out-of-stream variables' current values to the output record stream, e.g. @sum += $x; emit1 @sum which produces an extra record such as sum=3.1648382. These records, just like records from input file(s), participate in downstream then-chaining to other verbs.

For the first two options you are populating the output-records stream which feeds into the next verb in a then-chain (if any), or which otherwise is formatted for output using --o... flags.

For the last three options you are sending output directly to standard output, standard error, or a file.

Print statements

The print statement is perhaps self-explanatory, but with a few light caveats:

There are four variants: print goes to stdout with final newline, printn goes to stdout without final newline (you can include one using "\n" in your output string), eprint goes to stderr with final newline, and eprintn goes to stderr without final newline.
Output goes directly to stdout/stderr, respectively: data produced this way do not go downstream to the next verb in a then-chain. (Use emit for that.)
Print statements are for strings (print "hello"), or things which can be made into strings: numbers (print 3, print $a + $b), or concatenations thereof (print "a + b = " . ($a + $b)). Maps (in $*, map-valued out-of-stream or local variables, and map literals) as well as arrays are printed as JSON.
You can redirect print output to a file:

mlr --from myfile.dat put 'print > "tap.txt", $x'

You can redirect print output to multiple files, split by values present in various records:

mlr --from myfile.dat put 'print > $a.".txt", $x'

See also Redirected-output statements for examples.

Dump statements

The dump statement is for printing expressions, including maps, directly to stdout/stderr, respectively:

There are two variants: dump prints to stdout; edump prints to stderr.
Output goes directly to stdout/stderr, respectively: data produced this way do not go downstream to the next verb in a then-chain. (Use emit for that.)
You can use dump to output single strings, numbers, or expressions including map-valued data. Map-valued data are printed as JSON.
If you use dump (or edump) with no arguments, you get a JSON structure representing the current values of all out-of-stream variables.
As with print, you can redirect output to files.
See also Redirected-output statements for examples.

Tee statements

Records produced by a mlr put go downstream to the next verb in your then-chain, if any, or otherwise to standard output. If you want to additionally copy out records to files, you can do that using tee.

The syntax is, by example:

mlr --from myfile.dat put 'tee > "tap.dat", $*' then sort -n index

First is tee >, then the filename expression (which can be an expression such as "tap.".$a.".dat"), then a comma, then $*. (Nothing else but $* is teeable.)

You can also write to a variable file name -- for example, you can split a single file into multiple ones on field names:

mlr --csv cat example.csv

color,shape,flag,k,index,quantity,rate
yellow,triangle,true,1,11,43.6498,9.8870
red,square,true,2,15,79.2778,0.0130
red,circle,true,3,16,13.8103,2.9010
red,square,false,4,48,77.5542,7.4670
purple,triangle,false,5,51,81.2290,8.5910
red,square,false,6,64,77.1991,9.5310
purple,triangle,false,7,65,80.1405,5.8240
yellow,circle,true,8,73,63.9785,4.2370
yellow,circle,true,9,87,63.5058,8.3350
purple,square,false,10,91,72.3735,8.2430

mlr --csv --from example.csv put -q 'tee > $shape.".csv", $*'

mlr --csv cat circle.csv

color,shape,flag,k,index,quantity,rate
red,circle,true,3,16,13.8103,2.9010
yellow,circle,true,8,73,63.9785,4.2370
yellow,circle,true,9,87,63.5058,8.3350

mlr --csv cat square.csv

color,shape,flag,k,index,quantity,rate
red,square,true,2,15,79.2778,0.0130
red,square,false,4,48,77.5542,7.4670
red,square,false,6,64,77.1991,9.5310
purple,square,false,10,91,72.3735,8.2430

mlr --csv cat triangle.csv

color,shape,flag,k,index,quantity,rate
yellow,triangle,true,1,11,43.6498,9.8870
purple,triangle,false,5,51,81.2290,8.5910
purple,triangle,false,7,65,80.1405,5.8240

See also Redirected-output statements for examples.

Redirected-output statements

The print, dump tee, emit, emitp, and emitf keywords all allow you to redirect output to one or more files or pipe-to commands. The filenames/commands are strings which can be constructed using record-dependent values, so you can do things like splitting a table into multiple files, one for each account ID, and so on.

Details:

The print and dump keywords produce output immediately to standard output, or to specified file(s) or pipe-to command if present.

mlr help keyword print

print: prints expression immediately to stdout.

  Example: mlr --from f.dat put -q 'print "The sum of x and y is ".($x+$y)'
  Example: mlr --from f.dat put -q 'for (k, v in $*) { print k . " => " . v }'
  Example: mlr --from f.dat put  '(NR % 1000 == 0) { print > stderr, "Checkpoint ".NR}'

mlr help keyword dump

dump: prints all currently defined out-of-stream variables immediately
to stdout as JSON.

With >, >>, or |, the data do not become part of the output record stream but
are instead redirected.

The > and >> are for write and append, as in the shell, but (as with awk) the
file-overwrite for > is on first write, not per record. The | is for piping to
a process which will process the data. There will be one open file for each
distinct file name (for > and >>) or one subordinate process for each distinct
value of the piped-to command (for |). Output-formatting flags are taken from
the main command line.

  Example: mlr --from f.dat put -q '@v[NR]=$*; end { dump }'
  Example: mlr --from f.dat put -q '@v[NR]=$*; end { dump >  "mytap.dat"}'
  Example: mlr --from f.dat put -q '@v[NR]=$*; end { dump >> "mytap.dat"}'
  Example: mlr --from f.dat put -q '@v[NR]=$*; end { dump | "jq .[]"}'

mlr put sends the current record (possibly modified by the put expression) to the output record stream. Records are then input to the following verb in a then-chain (if any), else printed to standard output (unless put -q). The tee keyword additionally writes the output record to specified file(s) or pipe-to command, or immediately to stdout/stderr.

mlr help keyword tee

tee: prints the current record to specified file.
This is an immediate print to the specified file (except for pprint format
which of course waits until the end of the input stream to format all output).

The > and >> are for write and append, as in the shell, but (as with awk) the
file-overwrite for > is on first write, not per record. The | is for piping to
a process which will process the data. There will be one open file for each
distinct file name (for > and >>) or one subordinate process for each distinct
value of the piped-to command (for |). Output-formatting flags are taken from
the main command line.

You can use any of the output-format command-line flags, e.g. --ocsv, --ofs,
etc., to control the format of the output. See also mlr -h.

emit with redirect and tee with redirect are identical, except tee can only
output $*.

  Example: mlr --from f.dat put 'tee >  "/tmp/data-".$a, $*'
  Example: mlr --from f.dat put 'tee >> "/tmp/data-".$a.$b, $*'
  Example: mlr --from f.dat put 'tee >  stderr, $*'
  Example: mlr --from f.dat put -q 'tee | "tr \[a-z\\] \[A-Z\\]", $*'
  Example: mlr --from f.dat put -q 'tee | "tr \[a-z\\] \[A-Z\\] > /tmp/data-".$a, $*'
  Example: mlr --from f.dat put -q 'tee | "gzip > /tmp/data-".$a.".gz", $*'
  Example: mlr --from f.dat put -q --ojson 'tee | "gzip > /tmp/data-".$a.".gz", $*'

mlr put's emitf, emitp, and emit send out-of-stream variables to the output record stream. These are then input to the following verb in a then-chain (if any), else printed to standard output. When redirected with >, >>, or |, they instead write the out-of-stream variable(s) to specified file(s) or pipe-to command, or immediately to stdout/stderr.

mlr help keyword emitf

emitf: inserts non-indexed out-of-stream variable(s) side-by-side into the
output record stream.

With >, >>, or |, the data do not become part of the output record stream but
are instead redirected.

The > and >> are for write and append, as in the shell, but (as with awk) the
file-overwrite for > is on first write, not per record. The | is for piping to
a process which will process the data. There will be one open file for each
distinct file name (for > and >>) or one subordinate process for each distinct
value of the piped-to command (for |). Output-formatting flags are taken from
the main command line.

You can use any of the output-format command-line flags, e.g. --ocsv, --ofs,
etc., to control the format of the output if the output is redirected. See also mlr -h.

  Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf @a'
  Example: mlr --from f.dat put --oxtab '@a=$i;@b+=$x;@c+=$y; emitf > "tap-".$i.".dat", @a'
  Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf @a, @b, @c'
  Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf > "mytap.dat", @a, @b, @c'
  Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf >> "mytap.dat", @a, @b, @c'
  Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf > stderr, @a, @b, @c'
  Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf | "grep somepattern", @a, @b, @c'
  Example: mlr --from f.dat put '@a=$i;@b+=$x;@c+=$y; emitf | "grep somepattern > mytap.dat", @a, @b, @c'

Please see https://miller.readthedocs.io://johnkerl.org/miller/doc for more information.

mlr help keyword emitp

emitp: inserts an out-of-stream variable into the output record stream.
Hashmap indices present in the data but not slotted by emitp arguments are
output concatenated with ":".

With >, >>, or |, the data do not become part of the output record stream but
are instead redirected.

The > and >> are for write and append, as in the shell, but (as with awk) the
file-overwrite for > is on first write, not per record. The | is for piping to
a process which will process the data. There will be one open file for each
distinct file name (for > and >>) or one subordinate process for each distinct
value of the piped-to command (for |). Output-formatting flags are taken from
the main command line.

You can use any of the output-format command-line flags, e.g. --ocsv, --ofs,
etc., to control the format of the output if the output is redirected. See also mlr -h.

  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp @sums'
  Example: mlr --from f.dat put --opprint '@sums[$a][$b]+=$x; emitp > "tap-".$a.$b.".dat", @sums'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp @sums, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp >  "mytap.dat", @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp >> "mytap.dat", @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp | "gzip > mytap.dat.gz", @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp > stderr, @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emitp | "grep somepattern", @*, "index1", "index2"'

Please see https://miller.readthedocs.io://johnkerl.org/miller/doc for more information.

mlr help keyword emit

emit: inserts an out-of-stream variable into the output record stream. Hashmap
indices present in the data but not slotted by emit arguments are not output.

With >, >>, or |, the data do not become part of the output record stream but
are instead redirected.

The > and >> are for write and append, as in the shell, but (as with awk) the
file-overwrite for > is on first write, not per record. The | is for piping to
a process which will process the data. There will be one open file for each
distinct file name (for > and >>) or one subordinate process for each distinct
value of the piped-to command (for |). Output-formatting flags are taken from
the main command line.

You can use any of the output-format command-line flags, e.g. --ocsv, --ofs,
etc., to control the format of the output if the output is redirected. See also mlr -h.

  Example: mlr --from f.dat put 'emit >  "/tmp/data-".$a, $*'
  Example: mlr --from f.dat put 'emit >  "/tmp/data-".$a, mapexcept($*, "a")'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit @sums'
  Example: mlr --from f.dat put --ojson '@sums[$a][$b]+=$x; emit > "tap-".$a.$b.".dat", @sums'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit @sums, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit >  "mytap.dat", @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit >> "mytap.dat", @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit | "gzip > mytap.dat.gz", @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit > stderr, @*, "index1", "index2"'
  Example: mlr --from f.dat put '@sums[$a][$b]+=$x; emit | "grep somepattern", @*, "index1", "index2"'

Please see https://miller.readthedocs.io://johnkerl.org/miller/doc for more information.

Emit1 and emit/emitp/emitf

There are four variants: emit1, emitf, emit, and emitp. These are used to insert new records into the record stream -- or, optionally, redirect them to files.

Keep in mind that out-of-stream variables are a nested, multi-level map (directly viewable as JSON using dump), while Miller record values are as well during processing -- but records may be flattened down for output to tabular formats. See the page Flatten/unflatten: JSON vs. tabular formats for more information.

You can use emit1 to emit any map-valued expression, including $*, map-valued out-of-stream variables, the entire out-of-stream-variable collection @*, map-valued local variables, map literals, or map-valued function return values.
For emit, emitp, and emitf, you can emit map-valued local variables, map-valued field attributes (with $), map-va out-of-stream variables (with @), $*, @*, or map literals (with outermost {...}) -- but not arbitrary expressions which evaluate to map (such as function return values).

The reason for this is part historical and part technical. As we'll see below, you can do lots of syntactical things with emit, emitp, and emitf, including printing them side-by-side, index them, redirect the output to files, etc. What this means syntatically is that Miller's parser needs to handle all sorts of commas, parentheses, and so on:

  emitf @count, @sum
  emit @sum, "a", "b"
  emitp (@count, @sum),"a","b"}
  # etc

When we try to allow emitf/emit/emitp to handle arbitrary map-valued expressions, like mapexcept($*, mymap) and so on, this inserts more syntactic complexity in terms of commas, parentheses, and so on. The technical term is LR-1 shift-reduce conflicts, but we can simply think of this in terms of the parser not being able to efficiently disambiguate all the punctuational opportunities.

So, emit1 can handle syntactic richness in the one thing being emitted; emitf, emit, and emitp can handle syntactic richness in the side-by-side placement, indexing, and redirection.

(Mnemonic: If all you want is to insert a new record into the record stream, emit1 is probably the one you want.)

What this means is that if you want to emit an expression which evaluates to a map, you can do quite simply

mlr --c2p --from example.csv put -q '
  emit1 mapsum({"id": NR}, $*)
'

id color  shape    flag  k  index quantity rate
1  yellow triangle true  1  11    43.6498  9.8870
2  red    square   true  2  15    79.2778  0.0130
3  red    circle   true  3  16    13.8103  2.9010
4  red    square   false 4  48    77.5542  7.4670
5  purple triangle false 5  51    81.2290  8.5910
6  red    square   false 6  64    77.1991  9.5310
7  purple triangle false 7  65    80.1405  5.8240
8  yellow circle   true  8  73    63.9785  4.2370
9  yellow circle   true  9  87    63.5058  8.3350
10 purple square   false 10 91    72.3735  8.2430

And if you want indexing, redirects, etc., just assign to a temporary variable and use one of the other emit variants:

mlr --c2p --from example.csv put -q '
  o = mapsum({"id": NR}, $*);
  emit o;
'

id color  shape    flag  k  index quantity rate
1  yellow triangle true  1  11    43.6498  9.8870
2  red    square   true  2  15    79.2778  0.0130
3  red    circle   true  3  16    13.8103  2.9010
4  red    square   false 4  48    77.5542  7.4670
5  purple triangle false 5  51    81.2290  8.5910
6  red    square   false 6  64    77.1991  9.5310
7  purple triangle false 7  65    80.1405  5.8240
8  yellow circle   true  8  73    63.9785  4.2370
9  yellow circle   true  9  87    63.5058  8.3350
10 purple square   false 10 91    72.3735  8.2430

Emitf statements

Use emitf to output several out-of-stream variables side-by-side in the same output record. For emitf these mustn't have indexing using @name[...]. Example:

mlr put -q '
  @count += 1;
  @x_sum += $x;
  @y_sum += $y;
  end { emitf @count, @x_sum, @y_sum}
' data/small

count=5,x_sum=2.26476,y_sum=2.585083

Emit statements

Use emit to output an out-of-stream variable. If it's non-indexed you'll get a simple key-value pair:

cat data/small

a=pan,b=pan,i=1,x=0.346791,y=0.726802
a=eks,b=pan,i=2,x=0.758679,y=0.522151
a=wye,b=wye,i=3,x=0.204603,y=0.338318
a=eks,b=wye,i=4,x=0.381399,y=0.134188
a=wye,b=pan,i=5,x=0.573288,y=0.863624

mlr put -q '@sum += $x; end { dump }' data/small

{
  "sum": 2.26476
}

mlr put -q '@sum += $x; end { emit @sum }' data/small

sum=2.26476

If it's indexed then use as many names after emit as there are indices:

mlr put -q '@sum[$a] += $x; end { dump }' data/small

{
  "sum": {
    "pan": 0.346791,
    "eks": 1.140078,
    "wye": 0.777891
  }
}

mlr put -q '@sum[$a] += $x; end { emit @sum, "a" }' data/small

a=pan,sum=0.346791
a=eks,sum=1.140078
a=wye,sum=0.777891

mlr put -q '@sum[$a][$b] += $x; end { dump }' data/small

{
  "sum": {
    "pan": {
      "pan": 0.346791
    },
    "eks": {
      "pan": 0.758679,
      "wye": 0.381399
    },
    "wye": {
      "wye": 0.204603,
      "pan": 0.573288
    }
  }
}

mlr put -q '@sum[$a][$b] += $x; end { emit @sum, "a", "b" }' data/small

a=pan,b=pan,sum=0.346791
a=eks,b=pan,sum=0.758679
a=eks,b=wye,sum=0.381399
a=wye,b=wye,sum=0.204603
a=wye,b=pan,sum=0.573288

mlr put -q '@sum[$a][$b][$i] += $x; end { dump }' data/small

{
  "sum": {
    "pan": {
      "pan": {
        "1": 0.346791
      }
    },
    "eks": {
      "pan": {
        "2": 0.758679
      },
      "wye": {
        "4": 0.381399
      }
    },
    "wye": {
      "wye": {
        "3": 0.204603
      },
      "pan": {
        "5": 0.573288
      }
    }
  }
}

mlr put -q '
  @sum[$a][$b][$i] += $x;
  end { emit @sum, "a", "b", "i" }
' data/small

a=pan,b=pan,i=1,sum=0.346791
a=eks,b=pan,i=2,sum=0.758679
a=eks,b=wye,i=4,sum=0.381399
a=wye,b=wye,i=3,sum=0.204603
a=wye,b=pan,i=5,sum=0.573288

Now for emitp: if you have as many names following emit as there are levels in the out-of-stream variable's map, then emit and emitp do the same thing. Where they differ is when you don't specify as many names as there are map levels. In this case, Miller needs to flatten multiple map indices down to output-record keys: emitp includes full prefixing (hence the p in emitp) while emit takes the deepest map key as the output-record key:

mlr put -q '@sum[$a][$b] += $x; end { dump }' data/small

{
  "sum": {
    "pan": {
      "pan": 0.346791
    },
    "eks": {
      "pan": 0.758679,
      "wye": 0.381399
    },
    "wye": {
      "wye": 0.204603,
      "pan": 0.573288
    }
  }
}

mlr put -q '@sum[$a][$b] += $x; end { emit @sum, "a" }' data/small

a=pan,pan=0.346791
a=eks,pan=0.758679,wye=0.381399
a=wye,wye=0.204603,pan=0.573288

mlr put -q '@sum[$a][$b] += $x; end { emit @sum }' data/small

pan=0.346791
pan=0.758679,wye=0.381399
wye=0.204603,pan=0.573288

mlr put -q '@sum[$a][$b] += $x; end { emitp @sum, "a" }' data/small

a=pan,sum.pan=0.346791
a=eks,sum.pan=0.758679,sum.wye=0.381399
a=wye,sum.wye=0.204603,sum.pan=0.573288

mlr put -q '@sum[$a][$b] += $x; end { emitp @sum }' data/small

sum.pan.pan=0.346791,sum.eks.pan=0.758679,sum.eks.wye=0.381399,sum.wye.wye=0.204603,sum.wye.pan=0.573288

mlr --oxtab put -q '@sum[$a][$b] += $x; end { emitp @sum }' data/small

sum.pan.pan 0.346791
sum.eks.pan 0.758679
sum.eks.wye 0.381399
sum.wye.wye 0.204603
sum.wye.pan 0.573288

Use --flatsep to specify the character which joins multilevel keys for emitp (it defaults to a colon):

mlr --flatsep / put -q '@sum[$a][$b] += $x; end { emitp @sum, "a" }' data/small

a=pan,sum/pan=0.346791
a=eks,sum/pan=0.758679,sum/wye=0.381399
a=wye,sum/wye=0.204603,sum/pan=0.573288

mlr --flatsep / put -q '@sum[$a][$b] += $x; end { emitp @sum }' data/small

sum/pan/pan=0.346791,sum/eks/pan=0.758679,sum/eks/wye=0.381399,sum/wye/wye=0.204603,sum/wye/pan=0.573288

mlr --flatsep / --oxtab put -q '
  @sum[$a][$b] += $x;
  end { emitp @sum }
' data/small

sum/pan/pan 0.346791
sum/eks/pan 0.758679
sum/eks/wye 0.381399
sum/wye/wye 0.204603
sum/wye/pan 0.573288

Multi-emit statements

You can emit multiple map-valued expressions side-by-side by including their names in parentheses:

mlr --from data/medium --opprint put -q '
  @x_count[$a][$b] += 1;
  @x_sum[$a][$b] += $x;
  end {
      for ((a, b), _ in @x_count) {
          @x_mean[a][b] = @x_sum[a][b] / @x_count[a][b]
      }
      emit (@x_sum, @x_count, @x_mean), "a", "b"
  }
'

a   b   x_sum              x_count x_mean
pan pan 219.1851288316854  427     0.5133141190437597
pan wye 198.43293070748447 395     0.5023618498923658
pan eks 216.07522773165525 429     0.5036718595143479
pan hat 205.22277621488686 417     0.492140950155604
pan zee 205.09751802331917 413     0.4966041598627583
eks pan 179.96303047250723 371     0.48507555383425127
eks wye 196.9452860713734  407     0.4838950517724162
eks zee 176.8803651584733  357     0.49546320772681596
eks eks 215.91609712937984 413     0.5227992666570941
eks hat 208.783170520597   417     0.5006790659966355
wye wye 185.29584980261419 377     0.49150092785839306
wye pan 195.84790012056564 392     0.4996119901034838
wye hat 212.0331829346132  426     0.4977304763723314
wye zee 194.77404756708714 385     0.5059066170573692
wye eks 204.8129608356315  386     0.5306035254809106
zee pan 202.21380378504267 389     0.5198298297816007
zee wye 233.9913939194868  455     0.5142667998230479
zee eks 190.9617780631925  391     0.4883932942792647
zee zee 206.64063510417319 403     0.5127559183726382
zee hat 191.30000620900935 409     0.46772617655014515
hat wye 208.8830097609959  423     0.49381326184632596
hat zee 196.3494502965293  385     0.5099985721987774
hat eks 189.0067933716193  389     0.48587864619953547
hat hat 182.8535323148762  381     0.47993053101017374
hat pan 168.5538067327806  363     0.4643355557376876

What this does is walk through the first out-of-stream variable (@x_sum in this example) as usual, then for each keylist found (e.g. pan,wye), include the values for the remaining out-of-stream variables (here, @x_count and @x_mean). You should use this when all out-of-stream variables in the emit statement have the same shape and the same keylists.

Emit-all statements

Use emit all (or emit @* which is synonymous) to output all out-of-stream variables. You can use the following idiom to get various accumulators output side-by-side (reminiscent of mlr stats1):

mlr --from data/small --opprint put -q '
  @v[$a][$b]["sum"] += $x;
  @v[$a][$b]["count"] += 1;
  end{emit @*,"a","b"}
'

a   b   v.sum    v.count
pan pan 0.346791 1
eks pan 0.758679 1
eks wye 0.381399 1
wye wye 0.204603 1
wye pan 0.573288 1

mlr --from data/small --opprint put -q '
  @sum[$a][$b] += $x;
  @count[$a][$b] += 1;
  end{emit @*,"a","b"}
'

a   b   sum
pan pan 0.346791
eks pan 0.758679
eks wye 0.381399
wye wye 0.204603
wye pan 0.573288

a   b   count
pan pan 1
eks pan 1
eks wye 1
wye wye 1
wye pan 1

mlr --from data/small --opprint put -q '
  @sum[$a][$b] += $x;
  @count[$a][$b] += 1;
  end{emit (@sum, @count),"a","b"}
'

a   b   sum      count
pan pan 0.346791 1
eks pan 0.758679 1
eks wye 0.381399 1
wye wye 0.204603 1
wye pan 0.573288 1