Split a string into array from back

Question

I have a string.

var string = "31415926535897932384626433832795028841971693993751058209749445923078164";

I want to split it into an array of length 10 from back.

I have:

function split(a) {
  return a.split( /(?=(?:..........)*$)/ ).map(function(x){return parseInt(x)});
}

which gives me the desired output as:

[3, 1415926535, 8979323846, 2643383279, 5028841971, 6939937510, 5820974944, 5923078164]

Questions:

How do I make the above function dynamic so I can break strings to n number of characters? (Currently I am adding/removing dots)
How do I skip the first character when splitting? (I would like first element to be always 3 so second element can be of length 1 to n)?

Why would you overcomplicate some simple operations on string split by index into some compilcated regex? — SwiftMango
– SwiftMango, Commented Jul 20, 2015 at 5:06
@Derek朕會功夫 I tried having a variable like {n} but it didnot work. I found out we cant really pass variables in regex without using RegExp constructor. — WhatisSober
– WhatisSober, Commented Jul 20, 2015 at 5:38

Avinash Raj · Accepted Answer · 2015-07-20 05:30:55Z

6

Just specify the number of digits you want to get for each item inside curly braces. And note that you can't pass variable to the regex which uses / as delimiters. You have to use RegExp constructor to pass variables in regex.

var string = "31415926535897932384626433832795028841971693993751058209749445923078164";
function split(a,n) {
  return a.split( new RegExp("(?=(?:.{" + n + "})*$)" )).map(function(x){return parseInt(x)});
}
alert(split(string, 10))

OR

You may simply use match instead of split.

string.match(/(?!^.).{11}/gm)

DEMO

var string = "31415926535897932384626433832795028841971693993751058209749445923078164";
function split(a,n) {
  return a.match(new RegExp("(?!^.).{" + n + "}|^.", "gm")).map(function(x){return parseInt(x)});
}
alert(split(string, 11))

If you also want to match the remaining chars, ie, the char present at the start and the unmatched chars exists at the last, you may use this regex.

/(?!^.).{11}|^.|.+/gm

DEMO

edited Jul 20, 2015 at 5:30

answered Jul 20, 2015 at 5:01

Avinash Raj

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2 Comments

kieranpotts Over a year ago

This works perfectly for me. Great solution. In my jsfiddle I've wrapped it up in a helper function. jsfiddle.net/kieranpotts/8wjszvc5/1

WhatisSober Over a year ago

Perfect. Thank you Avinash. Much appreciated!

Harpreet Singh · Accepted Answer · 2015-07-20 05:16:53Z

1

Please check this

var _mySplit = function(str, splitLength) {
    var _regEx = '';
    var startSubStringLength = str.length % splitLength
    if(startSubStringLength > 0) {
        _regEx = new RegExp("(^.{1," + startSubStringLength + "})|(.{1," + splitLength +  "})|(.{1,})", "g")
    }
    return str.match(_regEx)
}

answered Jul 20, 2015 at 5:16

Harpreet Singh

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1 Comment

WhatisSober Over a year ago

Thanks Harpeet. I will do some performance testing later with and without regex when jsperf is back up.

Aniket Singh · Accepted Answer · 2015-07-20 05:52:39Z

1

the easy way..without using RegExp var string="31415926535897932384626433832795028841971693993751058209749445923078164"; var arr = new Array(); while (!string.length < 10) { substr = string.substr(strlen(string)-10); string = string.replace(substr, ''); arr.push(substr); } var result_arr = arr.reverse();

edited Jul 20, 2015 at 5:52

answered Jul 20, 2015 at 5:06

Aniket Singh

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2 Comments

kieranpotts Over a year ago

This is PHP rather than JavaScript. But if you could convert this to JS @Aniket, this would be the better answer probably, since it does not rely on regexes. What do you think? :)

WhatisSober Over a year ago

Thank you Aniket. jsperf is down at this time. I will do some performance testing with all the solutions when its back up.

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