[英]How to get index value of same array value in javascript
現在我有一個數組var a = [4,7,4]
在這個數組值 4 是相同的值,我怎樣才能獲得相同值的索引。
我在 StackOverflow 中有一些代碼,但它只檢查 num 2 值,我需要檢查每個元素並返回索引值。
JS:
var dataset = [2,2,4,2,6,4,7,8];
var results = [];
for ( i=0; i < dataset.length; i++ ){
if ( dataset[i] == 2 ){
results.push( i );
}
}
return results;
回答
var dataset = [2,2,4,2,6,4,7,8];
var results = [];
for ( i=0; i < dataset.length; i++ ){
for(j=i+1;j<dataset.length;j++){
if ( dataset[i] == dataset[j] ){
results.push( j );
break;
}
}
}
console.log(results);
此代碼背后的邏輯是檢查每個值與數組的其他值,以便可以找到重復值的索引。
使用reduce
構建查找:
const out = dataset.reduce((p, c, i) => {
// if the current value doesn't exist as a
// key in the object, add it and assign it an
// empty array
p[c] = (p[c] || []);
// push the index of the current element to its
// associated key array
p[c].push(i);
return p;
}, {});
OUTPUT
{
"2": [0, 1, 3],
"4": [2, 5],
"6": [4],
"7": [6],
"8": [7]
}
復制此代碼並在 console.log 上查看
console.log(Array.from({length: 50}, (v,i) => i));
對不起,在這里你可以看到: http://jsfiddle.net/42y08384/18/
var dataset = [2,2,4,2,6,4,7,8];
var results = {};
dataset.forEach(function(item, key) {
if(!results[item]) {
results[item] = [];
}
console.log(key)
results[item].push(key);
});
//results is an object where the key is the value from the dataset and the array within is the indexes where you can find them
for(key in results) {
console.log('Value ' + key + ' can be found in position '+ results[key].join(', ') )
}
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