javascript 获取重复的数组索引
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Get the array index of duplicates
提问by qwertyuiop
In a JavaScript array how can I get the index of duplicate strings?
在 JavaScript 数组中，如何获取重复字符串的索引？
Example:
例子：
MyArray = ["abc","def","abc"]; //----> return 0,2("abc");
Another example:
另一个例子：
My Array = ["abc","def","abc","xyz","def","abc"]
//----> return 0,2,5("abc") and 1,4("def");
I have no idea how to do this. Thanks in advance for your help!
我不知道该怎么做。在此先感谢您的帮助！
回答by Ingo Bürk
Yet another approach:
还有一种方法：
Array.prototype.getDuplicates = function () {
var duplicates = {};
for (var i = 0; i < this.length; i++) {
if(duplicates.hasOwnProperty(this[i])) {
duplicates[this[i]].push(i);
} else if (this.lastIndexOf(this[i]) !== i) {
duplicates[this[i]] = [i];
}
}
return duplicates;
};
It returns an object where the keys are the duplicate entries and the values are an array with their indices, i.e.
它返回一个对象，其中键是重复的条目，值是一个带有索引的数组，即
["abc","def","abc"].getDuplicates() -> { "abc": [0, 2] }
回答by Felix Kling
Another less sophisticated approach:
另一种不太复杂的方法：
Iterate over the whole array and keep track of the index of each element. For this we need a string -> positionsmap. An object is the usual data type to use for this. The keys are the elements of the array and the values are arrays of indexes/positions of each element in the array.
遍历整个数组并跟踪每个元素的索引。为此，我们需要一张string -> positions地图。对象是用于此目的的常用数据类型。键是数组的元素，值是数组中每个元素的索引/位置数组。
var map = {};
for (var i = 0; i < arr.length; i++) {
var element = arr[i]; // arr[i] is the element in the array at position i
// if we haven't seen the element yet,
// we have to create a new entry in the map
if (!map[element]) {
map[element] = [i];
}
else {
// otherwise append to the existing array
map[element].push(i);
}
// the whole if - else statement can be shortend to
// (map[element] || (map[element] = [])).push(i)
}
Now you can iterate over the map and remove all entries where the array value has a length of one. Those are elements that appear only once in an array:
现在您可以遍历映射并删除数组值长度为 1 的所有条目。这些元素在数组中只出现一次：
for (var element in map) {
if (map[element].length === 1) {
delete map[element];
}
}
Now mapcontains a string -> positionsmapping of all duplicate elements of the array. For example, if you array is ["abc","def","abc","xyz","def","abc"], then mapis an object of the form
现在map包含string -> positions数组的所有重复元素的映射。例如，如果您的数组是["abc","def","abc","xyz","def","abc"]，则map是形式的对象
var map = {
'abc': [0,2,5],
'def': [1,4]
};
and you can process it further in any way you like.
您可以以任何您喜欢的方式进一步处理它。
Further reading:
进一步阅读：
回答by EricG
This covers finding the indices efficiently:
这包括有效地查找索引：
var inputArray = [1, 2, 3, 4, 5, 6, 6, 7, 8, 9];
var encounteredIndices = {};
for(var i = 0; i < inputArray.length; i++)
if (encounteredIndices[inputArray[i]])
console.log(i); // Or add to some array if you wish
else
encounteredIndices[inputArray[i]] = 1;
