Parse multivalued JSON in GREL (OpenRefine)

A problem you have here is the difference between the cells that contain JSON arrays (i.e. multiple values) and those that don't.

There are different ways of approaching this issue, and the best approach may depend on how consistent the data is overall.

My first suggestion would be to use a filter or facet to work with the single value and array cells separately. Given the data you use in your example I think the following would work:

1) Create a Custom Text Facet on the column using the GREL

value.startsWith("[")

2) Select 'false' from the facet to work with the single value cells3) For these cells use the GREL

value.parseJson().resource

4) Select 'true' from the facet to work with the array cells5) For these cells use the GREL

forEach(value.parseJson(),v,v.resource)

(n.b. this is slightly different to the GREL you mention in your question as giving errors)

6) The output of this GREL is an OpenRefine array. You'll need to convert this to a string to store the output in a cell - so you may need to use something like:

forEach(value.parseJson(),v,v.resource).join("|")