ldj-pipe

This module enables quick creation of unix-style filters for line-delimited JSON.

For example, suppose we're given the following input:

{ "id": 0, "name": "Fred Jones", "age": 40, "sex": "M" }
{ "id": 1, "name": "Mary Jones", "age": 38, "sex": "F" }
{ "id": 2, "name": "Davy Jones", "age": 12, "sex": "M" }

... and desire the following output:

{ "id": 1, "first": "Fred", "last": "Jones" }
{ "id": 2, "first": "Mary", "last": "Jones" }
{ "id": 3, "first": "Davy", "last": "Jones" }

In other words, we want to ...

• increment each id attribute by one
• split the name attribute into first and last
• ignore everything else

We can use ldj-pipe to produce the needed filter:

pipe = require 'ldj-pipe'

filter = (d) ->

  # extract and transform incoming data element
  id = d.id + 1
  [first, last] = d.name.split ' '

  # return the set of desired attributes
  id:    id
  first: first
  last:  last

pipe.through filter

We can then use the resulting filter as follows:

cat in.ldj | filter.coffee > out.ldj

... or:

filter.coffee < in.ldj > out.ldj

See also

• logmap which uses JSONSelect selection syntax.

• jq