出现多次的数组值 [英] Array values that appear more than once

问题描述

我正在使用 lodash ，并且我有一个数组:

I'm using lodash and I have an array:

const arr = ['firstname', 'lastname', 'initials', 'initials'];

我想要一个仅包含多次出现的值(重复值)的新数组.

I want a new array containing only the values that appear more than once (the duplicate values).

似乎lodash可能有特定的方法，但是我看不到.像这样的const dups = _.duplicates(arr);会很好.

It seems like this is something lodash might have a specific method for, but I can't see one. Something like: const dups = _.duplicates(arr); would be nice.

我有:

// object with array values and number of occurrences
const counts = _.countBy(arr, value => value);

// reduce object to only those with more than 1 occurrence
const dups = _.pickBy(counts, value => (value > 1));

// just the keys
const keys = _.keys(dups);

console.log(keys); // ['initials']

有没有比这更好的方法了??

Is there a better way than this..?

推荐答案

此任务不必使用lodash，您可以使用

It's not necessary to use lodash for this task, you can easily achieve it using plain JavaScript with Array.prototype.reduce() and Array.prototype.indexOf():

var arr = ['firstname', 'lastname', 'initials', 'initials', 'a', 'c', 'a', 'a', 'c'];

var dupl = arr.reduce(function(list, item, index, array) { 
  if (array.indexOf(item, index + 1) !== -1 && list.indexOf(item) === -1) {
    list.push(item);
  }
  return list;
}, []);

console.log(dupl); // prints ["initials", "a", "c"]

检查有效的演示.

或者用lodash简化一点:

Or a bit simpler with lodash:

var arr = ['firstname', 'lastname', 'initials', 'initials', 'a', 'c', 'a', 'a', 'c'];

var dupl = _.uniq(_.reject(arr, function(item, index, array) { 
  return _.indexOf(array, item, index + 1) === -1; 
}));

console.log(dupl); // prints ["initials", "a", "c"]

这篇关于出现多次的数组值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！