js计算数组中某个元素重复出现的个数 |
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js返回一个数组某值出现的次数
输入：一个数组中某个元素的值 输出：需要计算该元素在数组中重复出现的个数 let counts = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0); console.log('数组counts中"李"出现的次数是：'+counts(["李","李","设","弟","弟","生","生","李"],"李"));结果：数组counts中"李"出现的次数是：3 有时候的根据需要需要计算数组中元素重复出现的个数 //统计一个数组中有多少个不重复的单词： // 不用reduce时： var arr = ["李","李","设","弟","弟","生","生","李"]; function getRepeatNum(){ var obj = {}; for(var i= 0, l = arr.length; i< l; i++){ var item = arr[i]; obj[item] = (obj[item] +1 ) || 1; } return obj; } console.log(getRepeatNum());结果：{李: 3, 设: 1, 弟: 2, 生: 2} // 用reduce时： var arr = ["李","李","设","弟","弟","生","生","李"]; function getRepeatNum(){ return arr.reduce(function(prev,next){ prev[next] = (prev[next] + 1) || 1; return prev; },{}); } console.log(getRepeatNum());结果：{李: 3, 设: 1, 弟: 2, 生: 2} |
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