How to round, floor, ceil, truncate

Some builds may lack those functions, but as far as I'm concerned floor is widely available; so, you can implement them using it.

round/0

def round: . + 0.5 | floor;

ceil/0

def ceil: if . | floor == . then . else . + 1.0 | floor end;

trunc/0

def trunc: if . < 0 then ceil else floor end;

In jq 1.6 you have access to round/ceil/floor functions

$ echo '{"mass": 188.72}' | jq ' .mass | round '189$ echo '{"mass": 188.72}' | jq ' .mass | ceil '189$ echo '{"mass": 188.72}' | jq ' .mass | floor '188$ 

For jq 1.5, here is the hack

Round:

$ echo '{"mass": 188.42}' | jq ' .mass + 0.5 | tostring | split(".") | .[0] '  -r188

Ceiling(may have to add more 9999s to increase precision):

$ echo '{"mass": 188.42}' | jq ' .mass + 0.99999999 | tostring | split(".") | .[0] '  -r189

Floor:

$ echo '{"mass": 188.42}' | jq ' .mass | tostring | split(".") | .[0] '  -r188

jq's math builtins are enumerated in the Math section of the jq Manual. The current release is at https://stedolan.github.io/jq/manual/;links to earlier versions are at the top.

Note that both jq 1.5 and 1.6 have builtins named round, ceil, floor and trunc: they are all 0-arity filters.

E.g.

[5.52, 5.50, -5.52 ] | map(trunc)#=> [5,5,-5]

Earlier versions of jq have different sets of Math functions, e.g. jq 1.4 has floor but not the other three.