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Split a String on 2nd last occurrence of comma in C#

I have a string say
var str = "xy,yz,zx,ab,bc,cd";
and I want to split it on the 2nd last occurrence of a comma in C# i.e
a = "xy,yz,zx,ab"
b = "bc,cd"
How can I achieve this result?

Let's find the required comma index with a help of LastIndexOf:
var str = "xy,yz,zx,ab,bc,cd";
// index of the 2nd last occurrence of ','
int index = str.LastIndexOf(',', str.LastIndexOf(',') - 1);
Then use Substring:
string a = str.Substring(0, index);
string b = str.Substring(index + 1);
Let's have a look:
Console.WriteLine(a);
Comsole.WriteLine(b);
Outcome:
xy,yz,zx,ab
bc,cd

Alternative "readable" approach ;)
const string text = "xy,yz,zx,ab,bc,cd";
var words = text.Split(',');
var firstBatch = Math.Max(words.Length - 2, 0);
var first = string.Join(",", words.Take(firstBatch));
var second = string.Join(",", words.Skip(firstBatch));
first.Should().Be("xy,yz,zx,ab"); // Pass OK
second.Should().Be("bc,cd"); // Pass OK

You could handle this via regex replacement:
var str = "xy,yz,zx,ab,bc,cd";
var a = Regex.Replace(str, #",[^,]+,[^,]+$", "");
var b = Regex.Replace(str, #"^.*,([^,]+,[^,]+)$", "$1");
Console.WriteLine(a);
Console.WriteLine(b);
This prints:
xy,yz,zx,ab
bc,cd

It you get Microsoft's System.Interactive extensions from NuGet then you can do this:
string output = String.Join(",", str.Split(',').TakeLast(2));

Remove trailing pipes - '|' in c#

I have a string that looks something like this:
"PID||000000|Z123345|23345|SOMEONE^FIRSTNAME^^^MISS^||150|F|1111||1 DREYFUS CLOSE^SOUTH CITY^COUNTY^^POST CODE^^^||0123 45678910^PRN^PH^^^^0123 45678910^^~^^CP^^^^^^~^NET^^^^^^^||||1A|||||A||||||||N||||||||||";
I am trying to remove any separating '|' characters after the 30th '|' in the string so that the output string looks like this:
"PID||000000|Z123345|23345|SOMEONE^FIRSTNAME^^^MISS^||150|F|1111||1 DREYFUS CLOSE^SOUTH CITY^COUNTY^^POST CODE^^^||0123 45678910^PRN^PH^^^^0123 45678910^^~^^CP^^^^^^~^NET^^^^^^^||||1A|||||A||||||||N";
I am trying to do it using as little code as possible, but not having much luck. Any help or ideas would be great.

You can use the TrimEnd method
string text = "stuff||||N||||||||||";
string result = text.TrimEnd('|'); //Result is stuff||||N

Brute force but only a little bit of code:
string s2 = string.Join("|", s1.Split('|').Take(31));
If you need any other processing of this kind of data (it looks like a kind of nested CSV) then string.Split() is useful to know.

string str = "PID||000000|Z123345|23345|SOMEONE^FIRSTNAME^^^MISS^||150|F|1111||1 DREYFUS CLOSE^SOUTH CITY^COUNTY^^POST CODE^^^||0123 45678910^PRN^PH^^^^0123 45678910^^~^^CP^^^^^^~^NET^^^^^^^||||1A|||||A||||||||N||||||||||";
int c = 0;
int after = 30;
StringBuilder newStr = new StringBuilder();
for(int i = 0;i < str.length; i++){
if(str[i] == '|'){
if(after != c){
newStr.append(str[i]);
c++;
}
}else{
newStr.append(str[i]);
}
}
results in
newStr == "PID||000000|Z123345|23345|SOMEONE^FIRSTNAME^^^MISS^||150|F|1111||1 DREYFUS CLOSE^SOUTH CITY^COUNTY^^POST CODE^^^||0123 45678910^PRN^PH^^^^0123 45678910^^~^^CP^^^^^^~^NET^^^^^^^||||1A|||||A||||||||N";

A regex should do the trick:
var regex = new Regex(#"^([^\|]*\|){0,30}[^\|]*");
var match = regex.Match(input);
if(match.Success)
{
var val = match.Value;
}

If what you really want is that everything after the 30th chunk loses its '|', then try:
var chunks = input.Split('|');
var output = String.Join('|',chunks.Take(30)) + String.Concat(chunks.Skip(30));
That said, I think it sounds like what you're really looking for is probably something like:
var output = input.TrimEnd('|');

// Get the indexes of all the | characters.
int[] pipeIndexes = Enumerable.Range(0, s.Length).Where(i => s[i] == '|').ToArray();
// If there are more than thirty pipes:
if (pipeIndexes.Length > 30)
{
// The former part of the string remains intact.
string formerPart = s.Substring(0, pipeIndexes[30]);
// The latter part needs to have all | characters removed.
string latterPart = s.Substring(pipeIndexes[30]).Replace("|", "");
s = formerPart + latterPart;
}

All elements before last comma in a string in c#

How can i get all elements before comma(,) in a string in c#?
For e.g.
if my string is say
string s = "a,b,c,d";
then I want all the element before d i.e. before the last comma.So my new string shout look like
string new_string = "a,b,c";
I have tried split but with that i can only one particular element at a time.

string new_string = s.Remove(s.LastIndexOf(','));

If you want everything before the last occurrence, use:
int lastIndex = input.LastIndexOf(',');
if (lastIndex == -1)
{
// Handle case with no commas
}
else
{
string beforeLastIndex = input.Substring(0, lastIndex);
...
}

Use the follwoing regex: "(.*),"
Regex rgx = new Regex("(.*),");
string s = "a,b,c,d";
Console.WriteLine(rgx.Match(s).Groups[1].Value);

You can also try:
string s = "a,b,c,d";
string[] strArr = s.Split(',');
Array.Resize(strArr, Math.Max(strArr.Length - 1, 1))
string truncatedS = string.join(",", strArr);

How to split for only one string without using arrays

I've a string 01-India. I want to split on '-' and get only the code 01. How can I do this. I'm a .net newbie. Split function returns a array. Since I need only one string, how can this be done. Is there a ingenious way to do it using split only. Or do I've to use substring only?

Other possibility is
string xy = "01-India";
string xz = xy.Split('-')[0];

You can search for the first occurence of - and then use the method substring to cut the piece out.
var result = input.Substring(0, input.IndexOf('-'))

string str = "01-India";
string prefix = null;
int pos = str.IndexOf('-');
if (pos != -1)
prefix = str.SubString(0,pos);

var str = "01-India";
var hyphenIndex = str.IndexOf("-");
var start = str.substring(0, hyphenIndex);
or you can use regular expression if it is a more complicated string pattern.

Something like this?
var s = "01-India";
var result = s.SubString(0, s.IndexOf("-"));

Since you don't want to use arrays, you could do an IndexOf('-') and then a substring.
string s = "01-India"
int index = s.IndexOf('-');
string code = s.Substring(0, index);
Or, for added fun, you could use String.Remove.
string s = "01-India"
int index = s.IndexOf('-');
string code = s.Remove(index);

string value = "01-India";
string part1 = value.Split('-')[0];

Strip prefix and value

if I have the string "freq1" or "freq12" and so on, how can I strip out freq and also the number by itself?

string foo = "freq12";
string fooPart = foo.Substring(4); // "12"
int fooNumber = int.parse(fooPart); // 12
if the "freq" part is not constant, then you can use regular expressions:
using System.Text.RegularExpressions;
string pattern = #"([A-Za-z]+)(\d+)";
string foo = "freq12";
Match match = Regex.Match(foo, pattern);
string fooPart = match.Groups[1].Value;
int fooNumber = int.Parse(match.Groups[2].Value);

Is it always going to be the text freq that prepends the number within the string? If so, your solution is very simple:
var str = "freq12";
var num = int.Parse(str.Substring(4));
Edit: Here's a more generic method in the case that the first part of the string isn't always "freq".
var str = "freq12";
int splitIndex;
for(splitIndex = 0; splitIndex < str.Length; splitIndex++)
{
if (char.IsNumeric(str[splitIndex]))
break;
}
if (splitIndex == str.Length)
throw new InvalidOperationException("The input string does not contain a numeric part.");
var textPart = int.Parse(str.Substring(0, splitIndex));
var numPart = int.Parse(str.Substring(splitIndex));
In the given example, textPart should evaluate to freq and numPart to 12. Let me know if this still isn't what you want.

Try something like this:
String oldString = "freq1";
String newString = oldString.Replace("freq", String.Empty);

If you know that the word "freq" will always be there, then you can do something like:
string number = "freq1".Replace("freq","");
That will result in "1".