I have a collection like this
List<int> {1,15,17,8,3};
how to get a flat string like "1-15-17-8-3" through LINQ query?
thank you
+9
A:
something like...
string mystring = string.Join("-", yourlist.Select( o => o.toString()).toArray()));
(Edit: Now its tested, and works fine)
Tim Jarvis
2009-07-07 23:04:19
If that works...I like it. Very short, sweet, and to the point!
Andrew Siemer
2009-07-07 23:05:10
This is the best answer. Note though, that the Join method used here has nothing to do with LINQ, it's a very useful method from the good old VB6 days....
andy
2009-07-07 23:12:09
Sure, the linq bit is just the conversion of the Int list to a string array via a select and a toArray()
Tim Jarvis
2009-07-07 23:13:21
True, but it doesn't answer how to do this through LINQ. With strings, I definitely would use this or StringBuilder, but seeing how this would be done the LINQ way would be a great introduction to using Aggregate (my solution using Aggregate is posted further down)
Charles
2009-07-07 23:54:23
A:
StringBuilder sb = new StringBuilder();
foreach(int i in collection)
{
sb.Append(i.ToString() + "-");
}
string result = sb.ToString().SubString(0,sb.ToString().ToCharArray().Length - 2);
Something like this perhaps (off the top of my head that is!).
Andrew Siemer
2009-07-07 23:04:35
+1
A:
You can write an extension method and then call .ToString("-") on your IEnumerable object type as shown here:
int[] intArray = { 1, 2, 3 };
Console.WriteLine(intArray.ToString(","));
// output 1,2,3
List<string> list = new List<string>{"a","b","c"};
Console.WriteLine(intArray.ToString("|"));
// output a|b|c
Examples of extension method implementation are here:
http://coolthingoftheday.blogspot.com/2008/09/todelimitedstring-using-linq-and.html http://www.codemeit.com/linq/c-array-delimited-tostring.html
AndrewDotHay
2009-07-07 23:15:03
+1
A:
Use Enumerable.Aggregate like so:
var intList = new[] {1,15,17,8,3};
string result = intList.Aggregate(string.Empty, (str, nextInt) => str + nextInt + "-");
This is the standard "LINQy" way of doing it - what you're wanting is the aggregate. You would use the same concept if you were coding in another language, say Python, where you would use reduce().
EDIT: That will get you "1-15-17-8-3-". You can lop off the last character to get what you're describing, and you can do that inside of Aggregate(), if you'd like:
string result = intList.Aggregate(string.Empty, (str, nextInt) => str + nextInt + "-", str => str.Substring(0, str.Length - 1));
The first argument is the seed, the second is function that will perform the aggregation, and the third argument is your selector - it allows you to make a final change to the aggregated value - as an example, your aggregate could be a numeric value and you want return the value as a formatted string.
HTH,
-Charles
Charles
2009-07-07 23:42:57
Actually I think this is what you wanted...myList.Select(o => o.ToString()).Aggregate((s1,s2) => s1 + "-" + s2);
Tim Jarvis
2009-07-07 23:53:53
Aggregate is a good answer, but I personally find its harder to understand than a simple string.join() (just my own personal pref)
Tim Jarvis
2009-07-07 23:56:14
If the list contains many elements then all those string concatenations will affect the performance. You could use a StringBuilder for the accumulator instead.
LukeH
2009-07-08 09:18:19
(By the way, your second version will throw an exception if the list is empty.)
LukeH
2009-07-08 09:26:45
@Tim: Nope `string result = intList.Aggregate(string.Empty, (str, nextInt) => str + nextInt + "-");` is correct. str is the "running total" - what's been aggregated thus far.
Charles
2010-02-04 00:48:29
@Luke: Good catch. You could check before hand, or use something like `str.Length - 1 > 0 ? : str.Length - 1 : 0` - but that's pretty ugly.
Charles
2010-02-04 00:51:22
A:
The best answer is given by Tim J.
If, however, you wanted a pure LINQ solution then try something like this (much more typing, and much less readable than Tim J's answer):
string yourString = yourList.Aggregate
(
new StringBuilder(),
(sb, x) => sb.Append(x).Append("-"),
sb => (sb.Length > 0) ? sb.ToString(0, sb.Length - 1) : ""
);
(This is a variation on Charles's answer, but uses a StringBuilder rather than string concatenation.)
LukeH
2009-07-08 09:16:33