How to make Javascript array unique by attribute
What is a quick way to create a unique Javascript array by attribute?
I have an array sorted by timestamp like:
[
{
ts: 1417048100,
release: 1.0
},
{
ts: 1417046900,
release: 1.1
},
{
ts: 1417046712,
release: 1.0
}
]
And I want to make it unique by issue number keeping only those with the most recent time stamp. In my example, this would mean deleting the last entry, since there is a newer one for this version.
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You can iterate over the array with forEach
and store the release numbers in an object to make sure all previously released iterations are collapsed from the array.
var arr = [{
ts: 1417048100,
release: 1.0
},
{
ts: 1417046900,
release: 1.1
},
{
ts: 1417046712,
release: 1.0
}];
var o = {};
arr.forEach(function(x, i) {
if (x.release in o) arr.splice(i, 1);
o[x.release] = null;
});
document.body.innerHTML = '<pre>' + JSON.stringify(arr, null, 4) + '</pre>';
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Convert it to a mapping using it release
as a key.
var output = {};
for(var i=0; i<input.length; i++) {
output[input[i].release] = input[i].ts;
}
It will automatically overwrite old keys with new release keys.
If you need it to be sorted, you will need to convert it to a list and sort, or filter the original list on only the remaining output keys.
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You can use Array.prototype.reduce along with Array.prototype.some , for example:
var items = [{ts: 1417048100,release: 1.0},{ts: 1417046900,release: 1.1},{ts: 1417046712,release: 1.0}];
var results = items.reduce(function(res, item){
var exists = res.some(function(t){ return (t.release === item.release );});
if (!exists){
res.push(item);
}
return res; },[]);
document.body.innerHTML = '<pre>' + JSON.stringify(results) + '</pre>';
Array.prototype.some allows you to check if an element exists in an array, and if it does, it is not included in Array.prototype.reduce res.push(item);
when processing the array.
If you are open to use in other libraries, you might be interested in checking out the unique uniqueness:
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if you can use jquery then try with grep
var releases =[
{
ts: 1417048100,
release: 1.0
},
{
ts: 1417046900,
release: 1.1
},
{
ts: 1417046712,
release: 1.0
}];
var newRelease={
ts: 1517046712,
release: 1.0
};
releases = jQuery.grep(y, function(value) {
return value.release != newRelease.release;
});
releases.push(newRelease);
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Try
var arr = [
{
ts: 1417048100,
release: 1.0
},
{
ts: 1417046900,
release: 1.1
},
{
ts: 1417046712,
release: 1.0
}
]
, arr = arr.sort(function(a, b) {
return (a.ts > b.ts) ? -1 : 1
}).filter(function(val, key) {
return $.inArray(val.release, arr.map(function(v) {return v.release})) === key
});
var arr = [
{
ts: 1417048100,
release: 1.0
},
{
ts: 1417046900,
release: 1.1
},
{
ts: 1417046712,
release: 1.0
}
]
, arr = arr.sort(function(a, b) {
return (a.ts > b.ts) ? -1 : 1
}).filter(function(val, key) {
return $.inArray(val.release, arr.map(function(v) {return v.release})) === key
});
$.each(arr, function(k, v) {
$("<span>").html("release:" + v.release + ", timestamp:" + v.ts + "<br />")
.appendTo("body")
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
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Converting an array to an associative array. The keys in an associative array are unique. Sample code shown in node.
→ node
> a ={ "1.0": 1417048100, "1.1": 1417046900}
{ '1.0': 1417048100,
'1.1': 1417046900 }
> a["1.0"]
1417048100
> a["1.0"]=99999
99999
> a
{ '1.0': 99999,
'1.1': 1417046900 }
For a better understanding, reading the hashes and the blog post below might also be helpful.
http://www.javascriptkata.com/2007/03/29/how-to-use-javascript-hashes/
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