Replace one of values in array if condition is true, in JMESPATH

Question

Here is JSON:

{
  "a": [
    "foo",
    "bar",
    "test"
  ]
}

The idea is to replace bar by bar_new, if bar is present in the array.

The desired output will be:

[
  "foo",
  "bar_new",
  "test"
] 

So, if we don't have bar in the input JSON, the output will be:

[
  "foo",
  "test"
]

I've tried to put it together by map() and join() functions, but join() function returns a string instead of an array.
I need exactly this array in the output.

Answer 1

Here is a solution, the only caveat is that it does not replace the element bar, it removes it out of the array and appends an element bar_new if there was an element bar in the first place.
So, effectively the element bar_new is not guaranteed to be at the same index as bar was.

---

In JMESPath you cannot do an if ... else ..., but you can apply the same principle as you will sometimes find in shell scripts where we can do

some_instruction \
  && another_instruction_when_the_first_one_is_successful \
  || yet_another_instruction_when_the_first_one_fail

So, in your case you can start by saying:

• if I find bar in the array, return me an altered version of the array:
  • without the value bar
  • with a new element bar_new
• if I don't find bar in the array (effectively, an else), return me the array in a

Finding an element in an array is quite simple, given that this is the role of the function contains().

Giving you a query like:

(contains(a, `bar`) && [`new_array_here`]) || a

Knowing how to append an element in an array is a tricky one, there is no easy concatenation between arrays in JMESPath, this said, you can create an array of arrays and flatten it.

For example:

[[`a`,`b`],`c`] | []

Would result in

[
  "a",
  "b",
  "c"
]

---

Combining all of this, the query

(contains(a, `bar`) && [a[? @ != `bar`], `bar_new`] | []) || a

Would yield, with your example JSON,

[
  "foo",
  "test",
  "bar_new"
]