From the source I am getting a JSON file with a nested structure. [start file] [ { "query": { "ids": [ 8016676 ], "dimensions": [ "ym:pv:date", "ym:pv:URLDomain", "ym:pv:URLPath" ], "metrics": [ "ym:pv:users" ], …

I think the parse is probably missing in the transform function, since you pass the data as an expression string it must be parsed first. exports.transform0 = function(options) { options = this.parse(options); return (options.data).map(data => { return { date: data.dimensions[0].name,…