You are data driving an API with your SOAtest test and you have data validation requirements on an array of data the API returns. This can be problematic because depending on the request parameters, which you've externalized into a data source, you will receive varying length arrays coming back in the API response. Since traditional data sources are two-dimensional (columns and rows), there is a problem because you have to account for a third dimension. Instead of hitting your head against the wall wondering how to construct multiple data source sheets to manage this hierarchy, there is a nice application of XPath that makes this problem easier to overcome.
Let's first take a look at how your data source can be constructed. This will also help to visualize the desired data validation described in the problem.
Here you can see I'm using a delimiting character '|' to separate the variable length accountIds I am expecting to see in my response depending on which data source row is being executed. Next, let's look at how the JSON Assertor in my SOAtest Test needs to be configured.
You can see the expected value is set to the Excel column that contains the delimiter we used. The magic that makes this validation possible is a customized XPath using the XPath function "string-join()".
Notice the string-join() function has two parameters. An XPath, and our delimiter String. You will want to start off with an XPath that locates all the accountIds in the response payload, and then use the string-join() function that will append your delimiting character in-between each node the XPath selects. If you want to learn more about the string-join() XPath function, see: https://www.w3schools.com/xml/xsl_functions.asp
And that's all it takes!