Searching through an array-CodePudding

Trying to learn how to think in jq script.

Given this data:

{
   "characters": [
       { "First": "Fred", "Last": "Weasley" },
       { "First": "George", "Last": "Weasley" },
       { "First": "Hermione", "Last": "Granger" },
       { "First": "Ron", "Last": "Weasley" },
       { "First": "Hagrid" },
       { "First": "Draco", "Last": "Malfoy" },
       { "First": "Molly", "Last": "Weasley" },
       { "First": "Voldemort" },
       { "First": "Lucius", "Last": "Malfoy" }
    ]
}

Find all characters with the same last name as "Ron". And no, you don't already know his last name.

CodePudding user response：

Find the last name you are looking for and save it in a variable, then update the characters array accordingly:

jq '
  (.characters[] | select(.First == "Ron").Last) as $last
  | .characters |= map(select(.Last == $last))
'

{
  "characters": [
    {
      "First": "Fred",
      "Last": "Weasley"
    },
    {
      "First": "George",
      "Last": "Weasley"
    },
    {
      "First": "Ron",
      "Last": "Weasley"
    },
    {
      "First": "Molly",
      "Last": "Weasley"
    }
  ]
}

Demo

If you want to make the call with a dynamic first name, provide it using a parameter variable:

jq --arg first "Ron" '
  (.characters[] | select(.First == $first).Last) as $last
  | .characters |= map(select(.Last == $last))
'

CodePudding user response：

You have an array of objects called "characters" each containing a "first" and "last" variable. Now to get the first one. Go characters[0].first which would return. "Fred" Or characters.[3].last would return "Weasley" Note the first entry in array is fetched by index 0. Make sense?