Step Functions - how to join an array?

Question

As of now there is a `States.StringSplit($.inputString, $.splitter)` intrinsic function to split an string into an array. 
Is there a way to join an array into an string? Something like `States.ArrayJoin($.inputString, $.joiner)`? 
Is there any work around to achieve something like that?

Reason is that I want to replace a character in a string, since there is no replace I thought about splitting and joining which does have the same effect. I'm using an activity and building an url with the taskToken, but unfortunately any "+" character get's replace by a space, so I want to replace it with "%2B".

Answer

Yes, but not easily.  You can iterate through the array of items you want to join using a Choice that flows to a Pass that uses States.Format to append each array item to a string.  It's ugly, but it works.

1. Create a Pass state that initializes the string accumulator and the number of items in the array, and flow to the Choice state below: Parameters: { "the_string": "", "item_count.$": "$.States.ArrayLength($.my_array)", "current_index": 0, "my_array.$": "$.my_array" }
2. Create a choice state that tests the array length and current index to see if any items remain to be appended: Choices: [ { "Variable": "$.current_index", "NumericLessThanPath": "$.item_count", "Next": "Append an Item" } ]
3. Create a Pass state that appends the string and increments the current index, and returns to the Choice state above: Parameters: { "the_string.$": "States.Format('{}your seprator here{}', $.the_string, $. )", "item_count.$": "$.item_count", "current_index.$": "States.MathAdd($.current_index, 1)", "my_array.$":"$.my_array" }

The Choice state will flow to the default Next state once all of the array items have been appended to $.the_string.

Hope that's clear enough.

Answer

One option will be to use States.Format() and pass the array contents if the array length is fixed.

Step Functions - how to join an array?

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