如何检查对象数组中两个相等的属性是否同时重复？

Question

I have the following objects array:

[
 { 
   homeGate: "gate_0",
   homeTerminal: "1",
   destinationGate: "gate_0",
   destinationTerminal: "2"   
 },
 { 
   homeGate: "gate_0",
   homeTerminal: "1",
   destinationGate: "gate_0",
   destinationTerminal: "3"   
 },
 { 
   homeGate: "gate_1",
   homeTerminal: "1",
   destinationGate: "gate_1",
   destinationTerminal: "2"   
 },
 { 
   homeGate: "gate_1",
   homeTerminal: "2",
   destinationGate: "gate_1",
   destinationTerminal: "3"   
 },
]

and I need to check which of the objects repeat the value "homeTerminal" and "destinationTerminal" at the same time. As we see in the example, I would need to retrieve the first and third objects that have the same value in both properties at the same time.

I tried to make a map, but I can only do it with one value and I don't know how to do it by checking two values at once. Thank you in advance.

Answer 1

var arr=[
 { 
   homeGate: "gate_0",
   homeTerminal: "1",
   destinationGate: "gate_0",
   destinationTerminal: "2"   
 },
 { 
   homeGate: "gate_0",
   homeTerminal: "1",
   destinationGate: "gate_0",
   destinationTerminal: "3"   
 },
 { 
   homeGate: "gate_1",
   homeTerminal: "1",
   destinationGate: "gate_1",
   destinationTerminal: "2"   
 },
 { 
   homeGate: "gate_1",
   homeTerminal: "2",
   destinationGate: "gate_1",
   destinationTerminal: "3"   
 },
]


var r=[];
    arr.forEach((element,index) => {
        for(let i=index;i<arr.length;i++){
            if(element.homeTerminal==arr[i].homeTerminal&&element.destinationGate==arr[i].destinationGate){
                if(!r.includes(element))r.push(element);
                if(!r.includes(arr[i]))r.push(arr[i]);
            }
        }
    });

that should work. You get the result in the r array

Answer 2

You can compute a lookup/map with compound keys consisting of the fields homeTerminal and destinationTerminal .

Then use that lookup to find repeating elements.

 const lkp = data.reduce((lkp, cur) => { const {homeTerminal, destinationTerminal} = cur; const key = `${homeTerminal}~~${destinationTerminal}`; lkp[key] = lkp[key] || []; lkp[key].push(cur); return lkp; }, {}); console.log (lkp); for (const key in lkp) { if (lkp[key].length > 1) console.log ("Duplicate entry", lkp[key]) }

 <script>var data = [ { homeGate: "gate_0", homeTerminal: "1", destinationGate: "gate_0", destinationTerminal: "2" }, { homeGate: "gate_0", homeTerminal: "1", destinationGate: "gate_0", destinationTerminal: "3" }, { homeGate: "gate_1", homeTerminal: "1", destinationGate: "gate_1", destinationTerminal: "2" }, { homeGate: "gate_1", homeTerminal: "2", destinationGate: "gate_1", destinationTerminal: "3" }, ]</script>

Answer 3

You can reduce the array to get the desired result.

 var arr = [{ homeGate: "gate_0", homeTerminal: "1", destinationGate: "gate_0", destinationTerminal: "2" }, { homeGate: "gate_0", homeTerminal: "3", destinationGate: "gate_0", destinationTerminal: "2" }, { homeGate: "gate_1", homeTerminal: "1", destinationGate: "gate_1", destinationTerminal: "2" }, { homeGate: "gate_2", homeTerminal: "1", destinationGate: "gate_2", destinationTerminal: "2" }, { homeGate: "gate_1", homeTerminal: "2", destinationGate: "gate_1", destinationTerminal: "3" }, { homeGate: "gate_1", homeTerminal: "3", destinationGate: "gate_1", destinationTerminal: "2" }] var result = arr.reduce((retArr, item) => { // condition to avoid duplication if (.retArr.includes(item)) { var filteredArr = arr.filter((i) => { return i.homeTerminal === item.homeTerminal && i.destinationTerminal === item;destinationTerminal; }). if (filteredArr.length > 1) retArr = [..,retArr. ..;filteredArr]; } return retArr, }; []). console;log(result);

reduce method of Array prototype takes 2 arguments:

1. A callback function which excutes for every element of the array.
2. Intial value for returning value
   1. This value must be returned from the callback function

callback function in turn takes 3 arguments:

1. return_value ( retArr )
2. array element ( item )
3. index not being used

Any operation can be done on the array element and the result must reflect in return_value (Contactenation operation here with spread values)

More on reduce https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce