I'd like avoid loop
I have this :
string s = "AAAA,12,BBBB,34,CCCCC,56";
With Linq, I'd like to have 2 List
In the first : AAAA, BBBB and CCCCC
In the second : 12,34 and 56
It's not based on numeric or not numeric.
Thanks,
8 Answers
You can use
var str = "AAAA,12,BBBB,34,CCCCC,56";
var spl = str.Split(',');
var l1 = spl.Where((x, y) => y % 2 == 0).ToList();
var l2 = spl.Where((x, y) => y % 2 == 1).ToList();
This is going to check if the index is even or odd.
Comments
Lets use Aggregate for the fun of it (and also, to prove this can be done as a single expression):
"AAAA,12,BBBB,34,CCCC,56".Split(',').Aggregate(
new { Uneven = new List<string>(), Even = new List<string>() },
(seed, s) => {
if (seed.Uneven.Count > seed.Even.Count)
seed.Even.Add(s);
else
seed.Uneven.Add(s);
return seed;
});
According to LINQPad, the result is this:
Of course I probably wouldn't do it this way, as it's kind of hard to read. And the testing for which list to append to is, well, not nice.
But at least we now have another example of lambda statements - normally the LINQ literature tries to forget them (probably because they won't work with SQL or any other backend that uses expression trees).
One advantage of this method as opposed to the cleaner solutions above is that this only makes one pass through the list. Since we are splitting a string, though, I'd try optimizing somewhere else ;) Wouldn't a IEnumerable<string> Split(this string self, string boundary) be cool?
4 Comments
Niki
Somehow it seems like a strange abuse of
Aggregate if the accumulator function modifies the the source parameter. It feels like following the letter of functional programming while contradicting the spirit. Am I the only one who thinks that?
Daren Thomas
@nikie with "source parameter" do you mean
TSource (not modified) or TAccumulate (modified, but isn't that always the case?)Daren Thomas
@gaearon, yes, this isn't really real-world, until you want to do a weighted average of a property for a list of objects. Then using
Aggregate like this can shine (especially since you can add a third parameter for returning/formatting the end result).Niki
I meant,
TAccumulate, of course. And I don't think it should be modified. For example, if I used Aggregate to calculate the sum or product of a list of numbers, the aggregateion function should just return the product or sum of it's arguments, without changing one. In this case, the "functional" solution (e.g. if you'd write it in Haskell or *ML) would probably work on linked lists and create a new linked list with a cheap Cons instruction instead of modifying its parameters. (IMO, Linq should have included a linked list type that allowed you to do just that.)Given that the rule is that you want every second string in one list and the others in another list, you can do something like this:
string s = "AAAA,12,BBBB,34,CCCCC,56";
var parts = s.Split(',');
var first = parts.Where((p, i) => i % 2 == 0);
var second = parts.Where((p, i) => i % 2 == 1);
answered Sep 29, 2010 at 12:15
Klaus Byskov Pedersen
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Comments
I'm not sure exactly what your end goal is, but you can try this:
var strings = s.Split(',').Where( (s,p) => p % 2 == 0)
Comments
Here is the isnumeric and not numeric filter for those interested... i realise its not needed
string x = "AAAA,12,BBBB,34,CCCCC,56";
Regex _isNumber = new Regex(@"^\d+$");
string[] y = x.Split(',') .Where(a => _isNumber.IsMatch(a)).ToArray();
string[] z =x.Split(',') .Where(a => !_isNumber.IsMatch(a)).ToArray();
Comments
you could group on the position and the extrat you lists from the group, like so:
public IEnumerable<IEnumerable<T>> ToLists<T>(IEnumerable<T> sequence)
{
var res = sequence.Select((item, position) => new { Item = item, Position = position })
.GroupBy(pair => pair.Position % 2 == 0,pair => pair.Item);
return from grouping in res
select grouping;
}
If you want the Lists to be of different types you can iterate through the result. Which is why the return type is not IEnumerable> but IEnumerable>. using ToList will iterate the sequence but if you want to perform some action on each element you might as well merge those actions, make one iteration through the sequnce superflourious
Comments
So much fun, without side-effects and no method calls.
"TesteDessaBudega".Aggregate(new List<List<char>>(),
(l, c) => char.IsUpper(c) ?
l.Union(
new List<List<char>>(){
new List<char>(){c}
}
).ToList() :
l.Take(l.Count - 1).Union(
new List<List<char>>(){
l.Last().Union(
new List<char>(){c}
).ToList()
}
).ToList()
)
Oh, on vbnet just for more fun.
"TesteDessaBudega".Aggregate(New List(Of List(Of Char))(),
Function(l, c) If(Char.IsUpper(c),
l.Union(
New List(Of List(Of Char))(New List(Of Char)(){
New List(Of Char)(New Char(){c})
})
).ToList(),
l.Take(l.Count - 1).Union(
New List(Of List(Of Char))(New List(Of Char)(){
l.Last().Union(
New List(Of Char)(New Char(){c})
).ToList()
})
).ToList()
))
1 Comment
btlog
Really unsure how this has any relevance to the question. I have a feeling you are answering a different question.
If the list is not ordered with every second being a number you could do something like this
var stringList = "AAAA,12,BBBB,34,CCCCC,56".Split(',');
var intsAsStrings = stringList.Where(
(x) =>
{
int i;
return int.TryParse(x, out i);
}).ToList();
var strings = stringList.Where(x => !intsAsStrings.Contains(x)).ToList();
I'd like avoid loopYou do realise that whatever LINQ solution you decide on will in fact, use at least one loop?