Why can't I produce unique objects array in this snippet?

Question

I have the following code snippet, where I want original array (filters) to be filtered and get unique filters array.

I think I tried all the methods possible and it (uniqueFilters array) is still same 11 member original array.

Whats wrong?

How can I ensure that this array is actually filtered down to just a few unique elements in it? (they all are coming from the same place and are the same)

UPDATE: - the answer successfully resolved the issue in js code. - in the actual app I had to also deal with typescript to use the suggested answer. So maybe will help someone:

let newUniqueFilters = Array.from(new Map(filters.map(f => [f._id, f] as [string, any])).values());

var filters = [{
	"_id": "filter1",
	"filterIndex": 1,
	"filterLabel": "Blur",
	"filterURL": "url(#filter1)",
	"filterEffects": [{
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 5
		}]
	}]
}, {
	"_id": "filter2",
	"filterIndex": 2,
	"filterLabel": "Shadow",
	"filterURL": "url(#filter2)",
	"filterEffects": [{
		"name": "feOffset",
		"attributes": [{
			"name": "dx",
			"value": 20
		}, {
			"name": "dy",
			"value": 20
		}, {
			"name": "result",
			"value": "offOut"
		}, {
			"name": "in",
			"value": "SourceAlpha"
		}]
	}, {
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 7
		}, {
			"name": "in",
			"value": "offOut"
		}, {
			"name": "result",
			"value": "blurOut"
		}]
	}, {
		"name": "feBlend",
		"attributes": [{
			"name": "mode",
			"value": "normal"
		}, {
			"name": "in2",
			"value": "blurOut"
		}, {
			"name": "in",
			"value": "SourceGraphic"
		}]
	}]
}, {
	"_id": "filter2",
	"filterIndex": 2,
	"filterLabel": "Shadow",
	"filterURL": "url(#filter2)",
	"filterEffects": [{
		"name": "feOffset",
		"attributes": [{
			"name": "dx",
			"value": 20
		}, {
			"name": "dy",
			"value": 20
		}, {
			"name": "result",
			"value": "offOut"
		}, {
			"name": "in",
			"value": "SourceAlpha"
		}]
	}, {
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 7
		}, {
			"name": "in",
			"value": "offOut"
		}, {
			"name": "result",
			"value": "blurOut"
		}]
	}, {
		"name": "feBlend",
		"attributes": [{
			"name": "mode",
			"value": "normal"
		}, {
			"name": "in2",
			"value": "blurOut"
		}, {
			"name": "in",
			"value": "SourceGraphic"
		}]
	}]
}, {
	"_id": "filter1",
	"filterIndex": 1,
	"filterLabel": "Blur",
	"filterURL": "url(#filter1)",
	"filterEffects": [{
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 5
		}]
	}]
}, {
	"_id": "filter1",
	"filterIndex": 1,
	"filterLabel": "Blur",
	"filterURL": "url(#filter1)",
	"filterEffects": [{
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 5
		}]
	}]
}, {
	"_id": "filter1",
	"filterIndex": 1,
	"filterLabel": "Blur",
	"filterURL": "url(#filter1)",
	"filterEffects": [{
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 5
		}]
	}]
}, {
	"_id": "filter2",
	"filterIndex": 2,
	"filterLabel": "Shadow",
	"filterURL": "url(#filter2)",
	"filterEffects": [{
		"name": "feOffset",
		"attributes": [{
			"name": "dx",
			"value": 20
		}, {
			"name": "dy",
			"value": 20
		}, {
			"name": "result",
			"value": "offOut"
		}, {
			"name": "in",
			"value": "SourceAlpha"
		}]
	}, {
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 7
		}, {
			"name": "in",
			"value": "offOut"
		}, {
			"name": "result",
			"value": "blurOut"
		}]
	}, {
		"name": "feBlend",
		"attributes": [{
			"name": "mode",
			"value": "normal"
		}, {
			"name": "in2",
			"value": "blurOut"
		}, {
			"name": "in",
			"value": "SourceGraphic"
		}]
	}]
}, {
	"_id": "filter1",
	"filterIndex": 1,
	"filterLabel": "Blur",
	"filterURL": "url(#filter1)",
	"filterEffects": [{
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 5
		}]
	}]
}, {
	"_id": "filter2",
	"filterIndex": 2,
	"filterLabel": "Shadow",
	"filterURL": "url(#filter2)",
	"filterEffects": [{
		"name": "feOffset",
		"attributes": [{
			"name": "dx",
			"value": 20
		}, {
			"name": "dy",
			"value": 20
		}, {
			"name": "result",
			"value": "offOut"
		}, {
			"name": "in",
			"value": "SourceAlpha"
		}]
	}, {
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 7
		}, {
			"name": "in",
			"value": "offOut"
		}, {
			"name": "result",
			"value": "blurOut"
		}]
	}, {
		"name": "feBlend",
		"attributes": [{
			"name": "mode",
			"value": "normal"
		}, {
			"name": "in2",
			"value": "blurOut"
		}, {
			"name": "in",
			"value": "SourceGraphic"
		}]
	}]
}, {
	"_id": "filter1",
	"filterIndex": 1,
	"filterLabel": "Blur",
	"filterURL": "url(#filter1)",
	"filterEffects": [{
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 5
		}]
	}]
}, {
	"_id": "filter2",
	"filterIndex": 2,
	"filterLabel": "Shadow",
	"filterURL": "url(#filter2)",
	"filterEffects": [{
		"name": "feOffset",
		"attributes": [{
			"name": "dx",
			"value": 20
		}, {
			"name": "dy",
			"value": 20
		}, {
			"name": "result",
			"value": "offOut"
		}, {
			"name": "in",
			"value": "SourceAlpha"
		}]
	}, {
		"name": "feGaussianBlur",
		"attributes": [{
			"name": "stdDeviation",
			"value": 7
		}, {
			"name": "in",
			"value": "offOut"
		}, {
			"name": "result",
			"value": "blurOut"
		}]
	}, {
		"name": "feBlend",
		"attributes": [{
			"name": "mode",
			"value": "normal"
		}, {
			"name": "in2",
			"value": "blurOut"
		}, {
			"name": "in",
			"value": "SourceGraphic"
		}]
	}]
}]

// first method:
var uniqueFilters = [];
for(let i = 0; i < filters.length; i++) {
    if(uniqueFilters.indexOf(filters[i]) == -1){
        uniqueFilters.push(filters[i])
    }
}
console.log("first method")
console.log("original array length:" + filters.length)
console.log("unique array length:" + uniqueFilters.length)

// second method:
//var uniqueFilters = filters.filter(function(elem, index, self) {
//        return index == self.indexOf(elem);
//});
//console.log("second method")
//console.log("original array length:" + filters.length)
//console.log("unique array length:" + uniqueFilters.length)

// suggested method 1:
var newUniqueFilters = Array.from(new Map(filters.map(f => [f._id, f])).values());
console.log(newUniqueFilters)

Object comparison is not based on object content, it's based on identity. An object is always !== every other object. — Pointy
– Pointy, Commented Mar 1, 2018 at 16:32

trincot · Accepted Answer · 2018-03-01 16:35:40Z

3

You can use a Map:

filters = Array.from(new Map(filters.map(f => [f._id, f])).values());

This assumes that it is enough to compare the _id values, which uniquely identify filters.

Note that comparing objects themselves (with indexOf or similar methods) will never show duplicates, as all the objects are different references (copies), even though they look the same. In general {} === {} is always false.

edited Mar 1, 2018 at 16:35

answered Mar 1, 2018 at 16:34

trincot

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5 Comments

Alex Over a year ago

Nice solution. But are there any advantages to passing it to a new instance of the Map class? Why not simply do: filters = filters.map(f => [f._id, f]); Is it for readability purposes?

trincot Over a year ago

@AlexanderEdwards, the new Map( ) will collapse items with the same id (i.e. with the same first value in the pairs), while the .map() alone will not reduce the number of items you get in your result.

Sergey Rudenko Over a year ago

Hey yo, this worked, but more importantly I wanted to thank you for explanation about objects comparison, now I see where my bugs are lol.

Sergey Rudenko Over a year ago

so feels like when it comes to objects - best practice is to ID those and then use that as a basis for copmparison.

trincot Over a year ago

Indeed, it is like that.

Dhaval · Accepted Answer · 2018-03-01 16:37:32Z

1

It's not working because every element in filter array has different memory location and object are compared by the memory location.

So every time you compare that object exist of filter array in uniqueFilters, it simply doesn't exist because every object has different memory location. so it will push every element in uniqueFilters.

answered Mar 1, 2018 at 16:37

Dhaval

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Comments

Wilson Madrid · Accepted Answer · 2018-03-01 16:35:15Z

0

Try changing this line

if(uniqueFilters.indexOf(filters[i]) == -1){ to if(uniqueFilters.indexOf(filters[i]) === -1){

If not worikingn you can too try comparing a specific attibute to all uniqueFilter

answered Mar 1, 2018 at 16:35

Wilson Madrid

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