Combining Two Arrays Based on Unique Identifier

Seeking guidance on enhancing this method to eliminate the need for a workaround.

I have two separate Object Arrays containing JSON data. The first array consists of all dates within a specific range, while the second array is derived from a SQL query, potentially lacking some months.

The desired output should be a sorted list of all months with a matterCount value assigned. However, when I utilize the function below, I encounter an issue where the matterCount is missing for months not present in the list.

I believe that there might be a small code snippet missing from the function causing this problem, but I am uncertain about the exact solution which led me here for help.

Although I have a workaround available on JSFiddle, I prefer cleaner and clearer code.

let x = [{labelDate: "Jun 2013"},
{labelDate: "Jul 2013"},
{labelDate: "Aug 2013"},
{labelDate: "Sep 2013"},
{labelDate: "Oct 2013"},
{labelDate: "Nov 2013"},
{labelDate: "Dec 2013"},
{labelDate: "Jan 2014"},
{labelDate: "Feb 2014"},
{labelDate: "Mar 2014"},
{labelDate: "Apr 2014"},
{labelDate: "May 2014"}];


let y = [{labelDate: "Jun 2013", matterCount: "1"},
{labelDate: "Jul 2013", matterCount: "2"},
{labelDate: "Aug 2013", matterCount: "2"},
{labelDate: "Sep 2013", matterCount: "10"},
{labelDate: "Oct 2013", matterCount: "1"},
{labelDate: "Nov 2013", matterCount: "1"},
{labelDate: "Feb 2014", matterCount: "1"},
{labelDate: "Apr 2014", matterCount: "17"},
{labelDate: "May 2014", matterCount: "21"}];

const merge = (x, y) =>
            x.map(xItem => ({
              ...y.find(yItem => yItem.labelDate === xItem.labelDate && Item),
              ...xItem
            }));

Actual outcome 
merge = [{labelDate: "Jun 2013", matterCount: "1"},
{labelDate: "Jul 2013", matterCount: "2"},
{labelDate: "Aug 2013", matterCount: "2"},
{labelDate: "Sep 2013", matterCount: "10"},
{labelDate: "Oct 2013", matterCount: "1"},
{labelDate: "Nov 2013", matterCount: "1"},
{labelDate: "Dec 2013"},
{labelDate: "Jan 2014"},
{labelDate: "Feb 2014", matterCount: "1"},
{labelDate: "Mar 2014"},
{labelDate: "Apr 2014", matterCount: "17"},
{labelDate: "May 2014", matterCount: "21"}];

desired outcome 
merge  = [{labelDate: "Jun 2013", matterCount: "1"},
{labelDate: "Jul 2013", matterCount: "2"},
{labelDate: "Aug 2013", matterCount: "2"},
{labelDate: "Sep 2013", matterCount: "10"},
{labelDate: "Oct 2013", matterCount: "1"},
{labelDate: "Nov 2013", matterCount: "1"},
{labelDate: "Dec 2013", matterCount: "0"},
{labelDate: "Jan 2014", matterCount: "0"},
{labelDate: "Feb 2014", matterCount: "1"},
{labelDate: "Mar 2014", matterCount: "0"},
{labelDate: "Apr 2014", matterCount: "17"},
{labelDate: "May 2014", matterCount: "21"}];

https://jsfiddle.net/cp39aoyf/2/

javascriptarraysecmascript-6

Answer №1

Have you considered using a default value with the logical OR operator:

const merge = (x, y) =>
        x.map(xItem => ({
          ...y.find(yItem => yItem.labelDate === xItem.labelDate && yItem) || {...xItem, matterCount: "0"}
        }));

Check out the demo on JSFiddle.

Alternatively, you could add the default value and allow it to be overridden by yItem:

const merge = (x, y) =>
    x.map(xItem => ({
      ...xItem,
      ...{matterCount: "0"},
      ...y.find(yItem => yItem.labelDate === xItem.labelDate && yItem)
    }));

Here's a Fiddle showcasing this approach.

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