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Operating on all fields

Bulk rename of fields

Suppose you want to replace spaces with underscores in your column names:

cat data/spaces.csv
a b c,def,g h i
123,4567,890
2468,1357,3579
9987,3312,4543

The simplest way is to use mlr rename with -g (for global replace, not just first occurrence of space within each field) and -r for pattern-matching (rather than explicit single-column renames):

mlr --csv rename -g -r ' ,_'  data/spaces.csv
a_b_c,def,g_h_i
123,4567,890
2468,1357,3579
9987,3312,4543
mlr --csv --opprint rename -g -r ' ,_'  data/spaces.csv
a_b_c def  g_h_i
123   4567 890
2468  1357 3579
9987  3312 4543

You can also do this with a for-loop:

cat data/bulk-rename-for-loop.mlr
map newrec = {};
for (oldk, v in $*) {
    newrec[gsub(oldk, " ", "_")] = v;
}
$* = newrec
mlr --icsv --opprint put -f data/bulk-rename-for-loop.mlr data/spaces.csv
a_b_c def  g_h_i
123   4567 890
2468  1357 3579
9987  3312 4543

Search-and-replace over all fields

How to do $name = gsub($name, "old", "new") for all fields?

cat data/sar.csv
a,b,c
the quick,brown fox,jumped
over,the,lazy dogs
cat data/sar.mlr
for (k in $*) {
  $[k] = gsub($[k], "e", "X");
}
mlr --csv put -f data/sar.mlr data/sar.csv
a,b,c
thX quick,brown fox,jumpXd
ovXr,thX,lazy dogs

Full field renames and reassigns

Using Miller 5.0.0's map literals and assigning to $*, you can fully generalize rename, reorder, etc.

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 '
  begin {
    @i_cumu = 0;
  }

  @i_cumu += $i;
  $* = {
    "z": $x + y,
    "KEYFIELD": $a,
    "i": @i_cumu,
    "b": $b,
    "y": $x,
    "x": $y,
  };
' data/small
z=0.346791,KEYFIELD=pan,i=1,b=pan,y=0.346791,x=0.726802
z=0.758679,KEYFIELD=eks,i=3,b=pan,y=0.758679,x=0.522151
z=0.204603,KEYFIELD=wye,i=6,b=wye,y=0.204603,x=0.338318
z=0.381399,KEYFIELD=eks,i=10,b=wye,y=0.381399,x=0.134188
z=0.573288,KEYFIELD=wye,i=15,b=pan,y=0.573288,x=0.863624