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add skip/2 as the counterpart to limit/2
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itchyny committed Sep 22, 2024
1 parent 860af44 commit 8ba7b1f
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Showing 5 changed files with 73 additions and 8 deletions.
14 changes: 12 additions & 2 deletions docs/content/manual/dev/manual.yml
Original file line number Diff line number Diff line change
Expand Up @@ -3037,16 +3037,26 @@ sections:
input: '[1,2,3]'
output: ['false']

- title: "`limit(n; exp)`"
- title: "`limit(n; expr)`"
body: |
The `limit` function extracts up to `n` outputs from `exp`.
The `limit` function extracts up to `n` outputs from `expr`.
examples:
- program: '[limit(3;.[])]'
input: '[0,1,2,3,4,5,6,7,8,9]'
output: ['[0,1,2]']

- title: "`skip(n; expr)`"
body: |
The `skip` function skips the first `n` outputs from `expr`.
examples:
- program: '[skip(3;.[])]'
input: '[0,1,2,3,4,5,6,7,8,9]'
output: ['[3,4,5,6,7,8,9]']

- title: "`first(expr)`, `last(expr)`, `nth(n; expr)`"
body: |
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21 changes: 18 additions & 3 deletions jq.1.prebuilt

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10 changes: 7 additions & 3 deletions src/builtin.jq
Original file line number Diff line number Diff line change
Expand Up @@ -149,10 +149,14 @@ def until(cond; next):
def _until:
if cond then . else (next|_until) end;
_until;
def limit($n; exp):
if $n > 0 then label $out | foreach exp as $item ($n; .-1; $item, if . <= 0 then break $out else empty end)
def limit($n; expr):
if $n > 0 then label $out | foreach expr as $item ($n; . - 1; $item, if . <= 0 then break $out else empty end)
elif $n == 0 then empty
else exp end;
else error("limit doesn't support negative count") end;
def skip($n; expr):
if $n > 0 then foreach expr as $item ($n; . - 1; if . < 0 then $item else empty end)
elif $n == 0 then expr
else error("skip doesn't support negative count") end;
# range/3, with a `by` expression argument
def range($init; $upto; $by):
if $by > 0 then $init|while(. < $upto; . + $by)
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32 changes: 32 additions & 0 deletions tests/jq.test
Original file line number Diff line number Diff line change
Expand Up @@ -334,6 +334,38 @@ null
"badness"
[1]

try limit(-1; error) catch .
null
"limit doesn't support negative count"

[skip(3; .[])]
[1,2,3,4,5,6,7,8,9]
[4,5,6,7,8,9]

[skip(3; .[])]
[]
[]

[skip(0; .[])]
[1,2,3]
[1,2,3]

[skip(2; .[])]
[1,2,3]
[3]

[skip(3; .[])]
[1,2,3]
[]

[skip(4; .[])]
[1,2,3]
[]

try skip(-1; error) catch .
null
"skip doesn't support negative count"

[first(range(.)), last(range(.))]
10
[0,9]
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4 changes: 4 additions & 0 deletions tests/man.test

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