Q:

How to convert a string to an integer in a JSON file using jq?

I use jq to transform a complex json object into a tinier one. My query is:
jq 'to_entries[]| {companyId: (.key), companyTitle: (.value.title), companyCode: (.value.booking_service_code)}' companies.json

Now, the (.key) is parsed as a string, yet I want companyId to be a number.
My result currently looks like this:
{
  "companyId": "1337",
  "companyTitle": "Some company title",
  "companyCode": "oxo"
}

yet it should be like:
{
  "companyId": 1337,
  "companyTitle": "Some company title",
  "companyCode": "oxo"
}

A:

jq has inbuilt functions, you can pipe your key to tonumber:
jq 'to_entries[]| {companyId: (.key)|tonumber, companyTitle: (.value.title), companyCode: (.value.booking_service_code)}' companies.json

As per the docs:

tonumber The tonumber function parses its input as a number. It will
  convert correctly-formatted strings to their numeric equivalent,
  leave numbers alone, and give an error on all other input.
Example jq '.[] | tonumber' Input   [1, "1"] Output 1 1

