使用正则表达式的Javascript数组排序

Question

I want to sort an array of phone numbers and have the length of the array outputted based on areacode. For example:

var nums = [
    8881756223,
    8881742341,
    9187221757,
    ...,
]

there are a lot more entries than that (roughly 1300) and its already in numerical order. However, what I want it to do is:

  1. look at the first 3 numbers of the first entry
  2. look at the next entries first 3 numbers
  3. if they are different, then splice the array, console.log new array.length 
  and console.log that area code

so for example, the first two numbers in the array i provided will be spliced into their new array, and the console output will be:

areacode: 888, length: 1
areacode: 918, length: 0

I know the regex to search for the first the numbers, but I don't exactly know how to splice them into their own arrays...Like i know, use splice, but comparing the two with logic statements, I've never had to do something like that before while using a regular expression.

what I have so far is this:

const patt = new RegExp('^\d{3}')

var newArr = nums.filter(x => patt)

for (var i = 0; i < newArr.length; i++)
    console.log(newArr[i])

but this is spitting out the full number, not the area code its self. Of course ill be adding the logic to sort after i get it to just spit out area codes.

Answer 1

you can try this

var nums = [
    8881756223,
    8881742341,
    9187221757
]

var prefixes = nums.map(x=>(x+"").substr(0,3));

var votes =  prefixes.reduce(
(votes, curr) => {
    if(votes[curr]) votes[curr]++;
    else {votes[curr] =1;}
    return votes;
}, {});

var ans = Object.keys(votes).map(x => ({areacode:x, length:votes[x]}));

console.log(ans);

ans will hold the value you require

vote counting technique i used is explained here https://igghub.github.io/2017/01/15/useful-js-reduce-trick/

Answer 2

I suggest using

nums.map(x => ("" + x).replace(/^(\d{3})[^]*/, '$1'))

Here,

• "" + x will coerce the number to string
• .replace(/^(\\d{3})[^]*/, '$1') will remove all chars keeping the first 3 digits (or the whole string upon no match).

JS Demo:

 var nums = [ 8881756223, 8881742341, 9187221757, 1 ]; var res = nums.map(x => ("" + x).replace(/^(\\d{3})[^]*/, '$1')); console.log(res);