DSL unset statements

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You can clear a map key by assigning the empty string as its value: $x="" or @x="". Using unset you can remove the key entirely. Examples:

<pre class="pre-highlight-in-pair"> <b>cat data/small</b> </pre> <pre class="pre-non-highlight-in-pair"> 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 </pre> <pre class="pre-highlight-in-pair"> <b>mlr put 'unset $x, $a' data/small</b> </pre> <pre class="pre-non-highlight-in-pair"> b=pan,i=1,y=0.726802 b=pan,i=2,y=0.522151 b=wye,i=3,y=0.338318 b=wye,i=4,y=0.134188 b=pan,i=5,y=0.863624 </pre>

This can also be done, of course, using mlr cut -x. You can also clear out-of-stream or local variables, at the base name level, or at an indexed sublevel:

<pre class="pre-highlight-in-pair"> <b>mlr put -q '@sum[$a][$b] += $x; end { dump; unset @sum; dump }' data/small</b> </pre> <pre class="pre-non-highlight-in-pair"> { "sum": { "pan": { "pan": 0.346791 }, "eks": { "pan": 0.758679, "wye": 0.381399 }, "wye": { "wye": 0.204603, "pan": 0.573288 } } } {} </pre> <pre class="pre-highlight-in-pair"> <b>mlr put -q '@sum[$a][$b] += $x; end { dump; unset @sum["eks"]; dump }' data/small</b> </pre> <pre class="pre-non-highlight-in-pair"> { "sum": { "pan": { "pan": 0.346791 }, "eks": { "pan": 0.758679, "wye": 0.381399 }, "wye": { "wye": 0.204603, "pan": 0.573288 } } } { "sum": { "pan": { "pan": 0.346791 }, "wye": { "wye": 0.204603, "pan": 0.573288 } } } </pre>

If you use unset all (or unset @* which is synonymous), that will unset all out-of-stream variables which have been assigned up to that point.