Scan string for numbers

Question

I have a string with words and numbers. How can i find the last number (the number of digits are unknown) and isolate it? Till now I used the Substring method, but the location of the number in the text, and also the length of the number, are unknown.

Thanks!

I advise you too look up here: http://stackoverflow.com/a/4734164/2524304 — Maxim Zhukov, Jul 26 '14 at 22:39
@user3057504 Can you please clarify, do you want the last _digit_ or the last _number_ that appears in the string? — fourpastmidnight, Jul 26 '14 at 22:57

p.s.w.g · Accepted Answer · 2014-07-26T22:54:19.317

Here's a simple solution using regular expressions:

var number = Regex.Match(input, @"(.*\D|^)(\d+)").Groups[2].Value;

Or a slightly different solution with a little bit of Linq thrown in for good measure:

var number = Regex.Matches(input, @"\d+").Cast<Match>().Last().Value;

And here's a solution using a plain old for loop; no Linq or regex required:

int start = 0, end = 0;
for (var i = input.Length - 1; i >= 0; i--) {
    if (char.IsDigit(input[i]))
    {
        end = i + 1;
        while (i >= 0 && char.IsDigit(input[i])) i--;
        start = i + 1;
        break;
    }
}
var number = input.Substring(start, end - start);

Tim Schmelter · Answer 2 · 2014-07-26T23:18:20.237

You could also use this combination of efficient string methods and readable LINQ:

string text = "Foo 1234 Test Bah344 ....";
int index = text.LastIndexOfAny("0123456789".ToCharArray());
if(index >= 0)
{
    string until = text.Substring(0, index + 1);
    var digits = until.Reverse().TakeWhile(char.IsDigit).Reverse();
    string lastNumber = new string(digits.ToArray());  // 344
}

Here's a one-and-a-half-liner which is not as efficient:

var lastDigits = text.Reverse()
    .SkipWhile(c => !char.IsDigit(c))
    .TakeWhile(char.IsDigit).Reverse();
string lastNumber = lastDigits.Any() ? new string(lastDigits.ToArray()) : "";

score 1 · Answer 3 · answered Jul 26 '14 at 22:42

1

You can also use the more explicit way:

var lastNumberIndex = yourString
        .LastIndexOfAny(new[] {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'});

answered Jul 26 '14 at 22:42

anderso

981
8
12

1

`"0123456789".ToCharArray()` is it better? :) – Maxim Zhukov Jul 26 '14 at 22:43
you have to cycle through your whole array at every char – Florian Leitgeb Jul 26 '14 at 22:46
2

But doesn't give the whole number _"How can i find the last number "_ – Tim Schmelter Jul 26 '14 at 22:48
@FSou1 even more resource cost. +1 Tim, Google digit vs number pls. – Martin Braun Jul 26 '14 at 22:55

score 1 · Answer 4 · answered Jul 26 '14 at 22:42

1

This should do it:

var res = Regex.Matches("kadlkfmg 57 dklfmgladg 89 dfdd", @"\d+");
var lastMatch = res.Cast<Match>().LastOrDefault();
if(lastMatch != null)
{
    var nr = lastMatch.Value;
}

answered Jul 26 '14 at 22:42

Magnus

45,362
8
80
118

Florian Leitgeb · Answer 5 · 2014-07-26T23:03:34.103

1

Simply start from the end and search for the first integer value you can find. In my opinion, this is the most performant way to do this.

For the last digit:

string s = "randomstringwithnumbers1234567890";
for (int i = s.Length() - 1; i >= 0; i--)
{
   if (int.tryParse(s[i], out n) //or use if (char.IsDigit(s[i]))
      return s[i];
}

For the last number:

string s = "randomstringwithnumbers1234567890";
string b = "";
for (int i = s.Length() - 1; i >= 0; i--) //or use if (char.IsDigit(s[i]))
{
   if (int.tryParse(s[i], out n)
      b =+ s[i];
   else if (b.Length() != 0)
      return b;
}

edited Jul 26 '14 at 23:03

answered Jul 26 '14 at 22:43

Florian Leitgeb

15,657
6
31
40

`s[i].GetType()` will return char. – Ash Burlaczenko Jul 26 '14 at 22:46
Aaah yes u were right. Changed to tryparse(). Its late here :) – Florian Leitgeb Jul 26 '14 at 22:50
This does not answer the OP's question sufficiently. As the number that should be returned is `1234567890`, not `0`. – fourpastmidnight Jul 26 '14 at 22:50
I am cycling through every character in the string, so the first one is "0". – Florian Leitgeb Jul 26 '14 at 22:52
@flol, I misunderstood the OP's question. I reversed my vote. Sorry for that!! – fourpastmidnight Jul 26 '14 at 22:53
Thank you. In my opinion, this should be the most performant way. What do you think? – Florian Leitgeb Jul 26 '14 at 22:54
@flol Well, it'll work. I'm not sure about _most_ performant. For example, is your code any more/less performant than @terrybozzio's answer: `var mychar2 = testing.Last(c => char.IsDigit(c))`? But it will work, so I voted it up. :) – fourpastmidnight Jul 26 '14 at 22:55
Hmm. I just read it. I do not know what is going under the hood at `IsDigit()`. The Lambda looks elegant :) – Florian Leitgeb Jul 26 '14 at 22:57
@flol, I think the OP mean the last number, not simply the last digit. Anyhow, `char.IsDigit` simply tests a character to see, if in the machine's local culture, the current character is a digit character. E.g. for en-US, 0, 1, 2, etc. are characters which are digits. – fourpastmidnight Jul 26 '14 at 22:59
Thanks for the explanation. I added a second version to check for the last number. – Florian Leitgeb Jul 26 '14 at 23:04

terrybozzio · Answer 6 · 2014-07-27T02:36:18.640

1

This will get the last digit in the string(both examples):

string testing = "SomeTextWith3Various45Numbers345InIt";
var mychar = testing.Reverse().First(c => char.IsDigit(c));
var mychar2 = testing.Last(c => char.IsDigit(c));

Edit:

To Get the Last number(whole) this will do:

var mychar3 = new string(testing.Reverse()
                                .SkipWhile(c => !char.IsDigit(c))
                                .TakeWhile(c => char.IsDigit(c))
                                .Reverse().ToArray());

edited Jul 27 '14 at 02:36

answered Jul 26 '14 at 22:48

terrybozzio

4,424
1
19
25

1

OP said last "number" – Martin Braun Jul 26 '14 at 22:59

Scan string for numbers

6 Answers6