Javascript swap characters in string

Question

Let's say I have a string like "abcabcabc" and I want the positions of 'a's and 'b's swapped so that I end up with "bacbacbac". What is the most elegant solution for this? (For the sake of this question I hereby define 'elegant' as fast and readable.)

I came up with

"abcabcabc".replace( /[ab]/g, function( c ){ return { 'a': 'b', 'b': 'a' }[ c ] } )

Which I neither regard fast nor readable. But now I wonder if there is a better way of doing it?

EDIT: The characters can be at any position. So the answer should hold for "xyza123buvwa456" (would be then "xyzb123auvwb456", too.

EDIT2: "swap" seems to be the wrong word. Replace all of a with b and all of b with a while both are single characters.

I throw in a couple of other ones:

"abcabcabc".replace( 'a', '_' ).replace( 'b','a' ).replace( '_', 'b' )

"abcabcabc".replace( /[ab]/g, function( c ){ return "ba".charAt( c.charCodeAt()-'a'.charCodeAt() ); } )

"abcabcabc".replace( /[ab]/g, function( c ){ return "ab".charAt( "ba".indexOf( c ) ) } )

I ended up using a modified version of Mark C.'s Answer:

"abcabcabc".replace( /[ab]/g, c => c == 'a' ? 'b' : 'a' )

So, how are you measuring performance that that code isn't fast? We need an object way to measure the answers or this is going to be opinion-based... — Heretic Monkey
– Heretic Monkey, Commented Feb 1, 2018 at 20:46
So this looks more like you are just replacing a with b and b with a rather than swapping. Is that actually intentional, because it's not quite the same thing. For example aaab -> bbba if you just replace, whereas if you swap you might expect baaa (or aaba your rules on swapping aren't clear here) — Matt Burland
– Matt Burland, Commented Feb 1, 2018 at 20:47
Possible duplicate of How do I swap substrings within a string? — Mark C.
– Mark C., Commented Feb 1, 2018 at 20:56

Mark C. · Accepted Answer · 2018-02-01 21:04:36Z

14

Try this :

str.replace(/[ab]/g, function($1) { return $1 === 'a' ? 'b' : 'a' })

example:

console.log("abcabcabc".replace(/[ab]/g, function($1) { return $1 === 'a' ? 'b' : 'a' }))

edited Feb 1, 2018 at 21:04

answered Feb 1, 2018 at 21:00

Mark C.

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3 Comments

Matt Burland Over a year ago

You don't need the pipe |. In fact, it shouldn't be there at all

Mark C. Over a year ago

@MattBurland Got it - I was trying a myriad of different combinations and TBH have been trying to learn RegEx throug SO. Thanks for your help

Scheintod Over a year ago

Thanks. I ended up with a slightly modified version but I think this is both the cleanest and fastest way of doing it. (At least if not someone finds a sane way of doing it without regex.)

CRice · Accepted Answer · 2018-02-01 21:07:37Z

4

You can swap them (if they're always adjacent) by using a split/join combo:

console.log("abcabcabc".split("ab").join("ba"))

And in keeping with the split/join method, here's a way to swap them as individual characters (although it becomes significantly less readable):

console.log("aabbccaabbcc".split("a").map(s => s.split("b").join("a")).join("b"));

edited Feb 1, 2018 at 21:07

answered Feb 1, 2018 at 20:49

CRice

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2 Comments

Scheintod Over a year ago

Thanks for your answer. I really like it's creative approach. But please see Edit.

CRice Over a year ago

@Scheintod I edited the answer with a way to swap non-adjacent characters, although I don't know if I'd recommend ever doing it that way (a regex replace is almost certainly more readable).

Leon Plata · Accepted Answer · 2018-02-01 20:49:44Z

1

replace function accepts a string as the second parameter.

"abcabcabc".replace( /ab/g, "ba")

edited Feb 1, 2018 at 20:49

answered Feb 1, 2018 at 20:47

Leon Plata

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2 Comments

Matt Burland Over a year ago

That will replace both a and b with ba

Dan Over a year ago

@MattBurland Not true. This works as expected if ab are always adjacent.

User · Accepted Answer · 2018-11-19 06:13:45Z

1

I use this method when I need to swap long list of characters\words\strings!

The method also prevents strings already replaced to be replaced again, Example:

String = "AAABBBCCC BBB"

Replace "AAABBBCCC" with "BBB", then, "BBB" with "DDD"

Final String = "BBB DDD"

Note that, only "BBB" from the original string is replaced to "DDD"! The "BBB" replaced from "AAABBBCCC" is not re-replaced to "DDD"!

edited Nov 19, 2018 at 6:13

answered Sep 13, 2018 at 1:45

User

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Comments

Ele · Accepted Answer · 2018-02-01 20:51:14Z

0

Use a direct replace using Regex:

var result = "abcabcabc".replace( /ab/g, "ba");
console.log(result);

edited Feb 1, 2018 at 20:51

answered Feb 1, 2018 at 20:50

Ele

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3 Comments

Ele Over a year ago

@MarkC. are you serius? I was writing the answer using the JS snippet tool [<>]

Ele Over a year ago

@MarkC. you're wrong, he posted a wrong answer and then modified it

Ele Over a year ago

@MarkC. look the versions of his answer, come on!

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