Transform, filter, and reduce arrays

Goal: Apply the usual map/filter/fold trio to arrays inside an mq query — useful once a query has collected values into a list and you need to post-process them.

Prerequisites: None.

Map: transform each element

$ mq -I null 'map([1, 2, 3, 4, 5], fn(x): x + 1;)'

[2, 3, 4, 5, 6]

Filter: keep elements matching a condition

$ mq -I null 'filter([5, 15, 8, 20, 3], fn(x): x > 10;)'

[15, 20]

Fold: combine elements into a single value

$ mq -I null 'fold([1, 2, 3, 4], 0, fn(acc, x): acc + x;)'

10

Notes

• These compose naturally with Markdown selectors — e.g. .h.depth | filter(fn(x): x <= 2;) to keep only the depths of h1/h2 headings collected across a document (with -A).