How to replace characters in a string in c#

Question

So the title might be a little misleading, but hear me out. It's not as simple as I worded it in the title.

So I have a string say,

String dna="ACTG";

I have to convert said string into it's complement form. To complement said string, I have to replace all occurrences of "A" to "T", "C" to "G", "T" to "A" and "G" to "C". So the complement of the String should look like this:

String dnaComplement="TGAC";

How do I do this properly? E.G.

String temp = dna.Replace("A", "T");
temp = temp.Replace("T", "A");
temp = temp.Replace("C", "G");
temp = temp.Replace("G", "C");

This would have the output:

TCTC

Which is wrong. I'm a beginner at C# and I know a little about programming with it. I'm used to using java.

How are you complements defined? i.e. do you have complemets for letters other than A, T, C, G defined as well? — Michal Hosala, Nov 26 '14 at 09:37
And because you can not program a simple beginner job now is "advanced"? OMG. Get real, please. The question is valid, but it is not advanced at all. — TomTom, Nov 26 '14 at 09:37
Michal, they are the base pairs that form DNA. So this alphabet only has 4 letters. The pairing is how DNA can be replicated during cell division. — Loofer, Nov 26 '14 at 11:22

score 4 · Accepted Answer · answered Nov 26 '14 at 09:37

4

Something like:

String dna="ACTG";
String dnaComplement = "";

foreach(char c in dna)
{
  if (c == 'A') dnaComplement += 'T';
  else if (c == 'C') dnaComplement += 'G';
 // and so long
}

answered Nov 26 '14 at 09:37

Leo Chapiro

13,678
8
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`+=`copies the string every time, which might cause efficiency problems. – Fabian S. Nov 26 '14 at 09:54

Michal Hosala · Answer 2 · 2014-11-26T10:15:32.010

2

You can use dictionary of complements and then use Linq Select:

var complements = new Dictionary<char, char>
    {
        { 'A', 'T' },
        { 'C', 'G' },
        { 'G', 'C' },
        { 'T', 'A' },
    };

var original = "TGAC";
var transformated = string.Concat(original.Select(c => (complements.ContainsKey(c)) ? complements[c] : c));

edited Nov 26 '14 at 10:15

answered Nov 26 '14 at 09:40

Michal Hosala

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Sjips · Answer 3 · 2014-11-26T09:40:44.213

Change the characters first to something else.

String temp = dna.Replace("A", "t");
temp = temp.Replace("T", "A");
temp = temp.Replace("t", "T");
temp = temp.Replace("C", "g");
temp = temp.Replace("G", "C");
temp = temp.Replace("g", "G");

This code from you:

String temp = dna.Replace("A", "T"); // A's are changed to T...
temp = temp.Replace("T", "A"); // ... but your just obtained 'T's are changed back to A
// ...

score 1 · Answer 4 · edited May 23 '17 at 12:00

1

I would do this:

var complement = dna.Select(c =>
{
    switch (c)
    {
        case 'A': return 'T';
        case 'T': return 'A';
        case 'C': return 'G';
        case 'G': return 'C';
        default: throw new ArgumentException(); // or whatever
    }
});

EDIT: With this you get an IEnumerbale<char>. To transform this back to a string see this Answer.

edited May 23 '17 at 12:00

Community

1
1

answered Nov 26 '14 at 09:49

Fabian S.

909
6
20

score 1 · Answer 5 · answered Nov 26 '14 at 10:26

I would do this:

var complements = new Dictionary<char, char>
{
    { 'A', 'T' },
    { 'C', 'G' },
    { 'G', 'C' },
    { 'T', 'A' },
};

string dna = "ACTG";

string dnaComplement =
    new string(
        dna
            .ToCharArray()
            .Select(x => complements[x])
            .ToArray());

score 0 · Answer 6 · answered Nov 26 '14 at 09:34

0

Replace with unique tokens so for example A-->l, T-->m C-->n G-->o. Now you can substitute for each token without changing any other - so L-->T etc.

answered Nov 26 '14 at 09:34

Simon N

27
3

score 0 · Answer 7 · answered Nov 26 '14 at 09:46

Each of the answers above is correct and solves your problem, but if you're going to do a lot of replacing frequently, consider using a StringBuilder. string.Replace() returns a new string instance every time you call it, the old instance becomes garbage and has to be collected. This can lead to a performance penalty for your app.

score 0 · Answer 8 · answered Nov 26 '14 at 10:32

Like Michal Hosala said, you have to make clear what is the definition of the complement. I will assume that you split the string in 2 equal parts and the first char in the first string is the complement of the first char in the second string.

I also treated the case when you have an odd number of chars, the complement of "ACXTG" will be "TGXAC".

string dna = "ACTG";
string dnaComplement = "";

if (dna.Length % 2 == 1)
    dnaComplement += dna[dna.Length / 2];
for (int i = 0; i < dna.Length / 2; i++)
    dnaComplement = dna[dna.Length - i - 1] + dnaComplement + dna[i];

How to replace characters in a string in c#

8 Answers8