[pkg/ottl] support joining a slice into a string

[gray-oni]

Component(s)

pkg/ottl

Is your feature request related to a problem? Please describe.

It would be great to be able to join a slice of strings/values into a string with a delimiter. I haven't found an easy way to do it with existing converters. (the closest functionality is Concat function but it doesn't support iteration through slice of values)

example: some of the target/exporting systems/platforms may expect input parameter(s) arrive as a string attribute with values separated by delimiter (e.g. Datadog ddtags)

Describe the solution you'd like

Join function should assemble a slice of values into a string with the provided delimiter.
.e.g. usage examples

• join(attributes["array.attribute"]) (e.g. with default delimiter "," )
• join(attribute["array.attribute"], ";")

statement example:

• set(attributes["string.attribute"], join(attributes["array.attribute"], ";"))

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• pkg/ottl: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley @edmocosta

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[edmocosta]

I think we can probably adapt the Concat function to also work with slice's paths/fields, so we don't need to create a new function for that.

[TylerHelmuth]

Concat's first parameter is a slice. What about it's implementation is not working?

Here is the e2e test of it taking a slice of strings and combining them with a delimiter

[edmocosta]

Concat's first parameter is a slice. What about it's implementation is not working?

It's the same issue described here: #37343 (comment).
In summary, It does work with literal values, but not with map paths (even if the underlying key data is a slice (example)).

[gray-oni]

hi @edmocosta @TylerHelmuth

I think we can probably adapt the Concat function to also work with slice's paths/fields, so we don't need to create a new function for that.

Yeah, Concat can be adapted, I don't know about what is an idiomatic approach for OTTL about adding a new func vs adapting existing one. Concat func looks focused on items that can correctly be represented as a string (via StringLikeGetter). I assume if we would want to adapt Concat probably it could be changed to accept an array of items which can be represented as a slice of strings (e.g. Getter which would return []string instead of *string) and those slices of strings flatten in one big slice before concatination (or something like that). Any thoughts what is the best approach could be here?