JavaScript regular expression

This is an ordinary tutorial, as well as my notes. The reason is that it is very interesting to see another solution to a problem, and at the same time, make some regular notes for easy understanding.

subject

My impression of this question is:
There is an array of [1,1,2,3,3,3,3,4,5,5,5,6,6]
Using js
Turn it into [[1,1],2,[3,3,3],4,[5,5,5]. [6,6]]

There are many solutions. I only list two

Solution 1

Our usual solution is:
Array nesting, put the array with the same value into a new array
Then, the number of nested arrays in the new array is determined and the value is returned to form a new array
The new array is the answer

 var arr = [1,1,2,3,3,3,3,4,5,5,5,6,6]; var tempArr = []; var result = []; var i,len,item,lastArr; for(i = 0,len = arr.length;i < len;i++){ item = arr[i]; lastArr = tempArr.slice(-1)[0]; if(!lastArr || lastArr[0] != item){ lastArr = []; tempArr.push(lastArr); } lastArr.push(item); } for(i=0,len=tempArr.length;i<len;i++){ item = tempArr[i]; result.push(item.length > 1 ? item : item[0]); } console.log(result);

Solution 2

If we use regularization, the solution is as follows:

 var arr = [1,1,2,3,3,3,3,4,5,5,5,6,6]; var result = "[" + (arr.toString() + ",") .replace(/(([^,]+,)\2+)/g,'[$1],') .replace(/,(]|$)/g,'$1') + "]"; console.log(JSON.parse(result));

In this way, it becomes very efficient. Regularly find out more than two positions with the same value, and insert []
Then print it out.

From this code, we can see that,
First string the array

 var result = "[" + (arr.toString() + ",") + "]";

become [1,1,2,3,3,3,3,4,5,5,5,6,6,]

Then match two to be the same value with each other []

 var result = "[" + (arr.toString() + ",") .replace(/(([^,]+,)\2+)/g,'[$1],') + "]";

Finally, find ] Surplus in front ,

 var result = "[" + (arr.toString() + ",") .replace(/(([^,]+,)\2+)/g,'[$1],') .replace(/,(]|$)/g,'$1') + "]";

JSON.parse(result) Convert to array object and print it

regular expression

Through Solution 2, we sometimes face some problems, but there are simpler solutions

Now let's add some regular knowledge points

Metacharacter

from .replace(/(([^,]+,)\2+)/g,'[$1],') In, the regular part is /(([^,]+,)\2+)/g

The first "/" and the last "/" are separators, representing the beginning and end of the regular expression

Here is a description of metacharacters

sign

The last "g" flag indicates the global status used by the regular expression. Using the global flag indicates that the search operation in the searched string will find all matching items, not just the first one. This is also called global matching [Related flags include i (ignoreCase, meaning ignore case) and m (multiline, meaning cross row is allowed)], as shown in the following table

Add a sign

qualifier

Then let's look at the main part in the middle (([^,]+,)\2+)

Character groups are [] (square brackets) list all possible matches, + It means matching the previous expression one or more times,

Supplement a lower limit identifier

.replace(/(([^,]+,)\2+)/g,'[$1],') In $1 Replace the matched part with [$1] ,

The matching part is worth more than two identical values

.replace(/,(]|$)/g,'$1') Is to go ,] In ,

Well written···

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