jq: error: round/0 is not defined at <top-level> - json

Question

round function in jq doesn't work.
$ jq '10.01 | round'
jq: error: round/0 is not defined at <top-level>, line 1:
10.01 | round
jq: 1 compile error
$ jq --help
jq - commandline JSON processor [version 1.5-1-a5b5cbe]
What I need to do?

Answer 1

Seems like round is unavailable in your build. Either upgrade jq or implement round using floor:
def round: . + 0.5 | floor;
Usage example:
$ jq -n 'def round: . + 0.5 | floor; 10.01 | round'
10

Answer 2

We can use the pow function along with . + 0.5 | floor to create our own 'round' function that takes a value to round as input and the number of decimal places as argument.
def round_whole:
# Basic round function, returns the closest whole number
# Usage:
# 2.6 | round_whole // 3
. + 0.5 | floor
;
def round(num_dec):
# Round function, takes num_dec as argument
# Usage: 2.2362 | round(2) // 2.24
num_dec as $num_dec |
# First multiply the number by the number of decimal places we want to round to
# i.e 2.2362 becomes 223.62
. * pow(10; $num_dec) |
# Then use the round_whole function
# 223.62 becomes 224
round_whole |
# Then divide by the number of decimal places we want to round by
# 224 becomes 2.24 as expected
. / pow(10; $num_dec)
;
jq --null-input --raw-output \
'
def round_whole:
# Basic round function, returns the closest whole number
# Usage:
# 2.6 | round_whole // 3
. + 0.5 | floor
;
def round(num_dec):
# Round function, takes num_dec as argument
# Usage: 2.2362 | round(2) // 2.24
num_dec as $num_dec |
# First multiply the number by the number of decimal places we want to round to
# i.e 2.2362 becomes 223.62
. * pow(10; $num_dec) |
# Then use the round_whole function
# 223.62 becomes 224
round_whole |
# Then divide by the number of decimal places we want to round by
# 224 becomes 2.24 as expected
. / pow(10; $num_dec)
;
[
2.2362,
2.4642,
10.23423
] |
map(
round(2)
)
'
Yields
[
2.24,
2.46,
10.23
]