I have below array of objects,
var data = [
{
label: "Book1",
data: "US edition"
},
{
label: "Book1",
data: "UK edition"
},
{
label: "Book2",
data: "CAN edition"
}
];
I want to merge the duplicate objects based on attribute ‘label’ so that Final output will look like below,
var data = [
{
label: "Book1",
data: ["US edition", "UK edition"] //data attribute is merged
},
{
label: "Book2",
data: "CAN edition"
}
];
Can someone help me identify the approach?
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Answer
I would probably loop through with filter
, keeping track of a map of objects I’d seen before, along these lines (edited to reflect your agreeing that yes, it makes sense to make (entry).data
always an array):
var seen = {};
data = data.filter(function(entry) {
var previous;
// Have we seen this label before?
if (seen.hasOwnProperty(entry.label)) {
// Yes, grab it and add this data to it
previous = seen[entry.label];
previous.data.push(entry.data);
// Don't keep this entry, we've merged it into the previous one
return false;
}
// entry.data probably isn't an array; make it one for consistency
if (!Array.isArray(entry.data)) {
entry.data = [entry.data];
}
// Remember that we've seen it
seen[entry.label] = entry;
// Keep this one, we'll merge any others that match into it
return true;
});
In an ES6 environment, I’d use seen = new Map()
rather than seen = {}
.
Note: Array.isArray
was defined by ES5, so some quite older browsers like IE8 won’t have it. It can easily be shimmed/polyfilled, though:
if (!Array.isArray) {
Array.isArray = (function() {
var toString = Object.prototype.toString;
return function(a) {
return toString.call(a) === "[object Array]";
};
})();
}
Side note: I’d probably also always make (We’ve done that above now.)entry.data
an array, even if I didn’t see two values for it, because consistent data structures are easier to deal with. I didn’t do that above because your end result showed data
being just a string when there was only one matching entry.
Live example (ES5 version):
var data = [
{
label: "Book1",
data: "US edition"
},
{
label: "Book1",
data: "UK edition"
},
{
label: "Book2",
data: "CAN edition"
}
];
snippet.log("Before:");
snippet.log(JSON.stringify(data, null, 2), "pre");
var seen = {};
data = data.filter(function(entry) {
var previous;
// Have we seen this label before?
if (seen.hasOwnProperty(entry.label)) {
// Yes, grab it and add this data to it
previous = seen[entry.label];
previous.data.push(entry.data);
// Don't keep this entry, we've merged it into the previous one
return false;
}
// entry.data probably isn't an array; make it one for consistency
if (!Array.isArray(entry.data)) {
entry.data = [entry.data];
}
// Remember that we've seen it
seen[entry.label] = entry;
// Keep this one, we'll merge any others that match into it
return true;
});
snippet.log("After:");
snippet.log(JSON.stringify(data, null, 2), "pre");
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