集体记忆
lodash.js->Array->difference
用法
返回一个去重后的数组,每个值不蕴含在其余数组参数中。后果值的程序是由第一个数组中的程序确定。
例子
_.difference([1,2,3],[3],[1,5])
//==>[2];
源码了解
difference(array, values, iteratee, comparator) {
var index = -1,
includes = arrayIncludes,
isCommon = true,
length = array.length,
result = [],
valuesLength = values.length;
if (!length) {
return result;
}
if (iteratee) {
values = arrayMap(values, baseUnary(iteratee));
}
if (comparator) {
includes = arrayIncludesWith;
isCommon = false;
}
else if (values.length >= LARGE_ARRAY_SIZE) {
includes = cacheHas;
isCommon = false;
values = new SetCache(values);
}
outer:
while (++index < length) {
var value = array[index],
computed = iteratee ? iteratee(value) : value;
if (isCommon && computed === computed) {
var valuesIndex = valuesLength;
while (valuesIndex--) {
if (values[valuesIndex] === computed) {
continue outer;
}
}
result.push(value);
}
else if (!includes(values, computed, comparator)) {
result.push(value);
}
}
return result;
}
1.外围代码
outer:
while (++index < length) {
var value = array[index],
computed = iteratee ? iteratee(value) : value;
if (isCommon && computed === computed) {
var valuesIndex = valuesLength;
while (valuesIndex--) {
if (values[valuesIndex] === computed) {
continue outer;
}
}
result.push(value);
}
else if (!includes(values, computed, comparator)) {
result.push(value);
}
}
return result;
`思路:`将除array之外的数组参数合并去重,失去values,再应用includes办法,判断array中的元素是否存在于values中,若不存在行将value放进新数组result中,最初返回result。
延申
假如有一需要,重点展现本月在本年没有呈现过的新呈现的天气类型:
difference(month12,month1,month2.....);
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