Not able to write simple DSL for loops: take value from previous record

[aborruso]

Hi,
I have a simple goal: to have a new field in which I have the value of the previous record of another field.

Starting from

field
a
b
a

to have

field,out
a,
b,a
a,b

I have written this wrong script.

mlr --csv put -S '@start="";
  for (key, value in $*){
    if(@start==""){$out=""}
  else{$out=@start;@start=$field};
};' input.csv

I think I must add some emit and end but I'm not able to think about them 😢

[aborruso]

Solved, I'm stupid :(

mlr --csv put -S '
begin {
  @start = "";
}
for (key, value in $*){
  if(@start=="") {
    $out="";
    @start=$field
  }
  else {
    $out=@start;
    @start=$field
  };
};'  input.csv

field,out
a,
b,a
a,b

[johnkerl]

@aborruso nice! See also mlr step -a shift, just FYI :)

[aborruso]

I'm really stupid :D

Thank you