Iterating over arrays simultaneously using jq

user_4162799 0
Viewed 65

I'm describing the output I'd like to have using jq

Here my json file

{
  "partitions": [
    {
      "replicas": [
        0,
        1,
        2
      ],
      "log_dirs": [
        "any",
        "any",
        "any"
      ]
    },
    {
      "replicas": [
        2,
        0,
        1
      ],
      "log_dirs": [
        "any",
        "any",
        "any"
      ]
    },
[...]

I would like, for every object in partitions[] to replace the value of the i th string in log_dirs[] by its concatenation with the i th number in replicas[] in order to have something like this

{
  "partitions": [
    {
      "replicas": [
        0,
        1,
        2
      ],
      "log_dirs": [
        "any0",
        "any1",
        "any2"
      ]
    },
    {
      "replicas": [
        2,
        0,
        1
      ],
      "log_dirs": [
        "any2",
        "any0",
        "any1"
      ]
    },
[...]
jq arrays loops json
2 Answers

Use a reduce loop with a range

.partitions[] |= reduce range(0; ( .replicas | length ) ) as $r 
  ( . ; .log_dirs[$r] += ( .replicas[$r] | tostring ) )

The reduce expression works by iterating over the entire log_dirs array upto the length of replicas list and modifying each entry .log_dirs[$r] (here r runs from 0 - length of replicas) by appending the corresponding value at replicas[$r]. Since replicas contains numerics, it needs to be converted to string for the append operation.

jqplay - demo

user_52910150

I'm not quite happy with this, but it does work:

jq '.partitions[] |= . + (
  . as $p | {
    log_dirs: [
      range(.replicas | length) |
      "\($p.log_dirs[.])\($p.replicas[.])"
    ]
  }
)' in.json
user_1529480
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