Mapping list of items to shortest starting string in list

Question

I have a list of 5 arbitrary user-inputted strings:

List<string> original = new List<string>() {"a", "a1", "a2", "b", "b1"} ;

For each string in the original collection, I want to get back the shortest string in the list which starts the current string:

"a" -> "a"
"a1" -> "a"
"a2" -> "a"
"b" -> "b"
"b1" -> "b"

How can I do this using LINQ?

Some more examples:

{a, ghjkjajj,hkj,bn,n} => {a, ghjkjajj,hkj,bn,n}
{ghj465,abn,abn1,hj,ui} => {ghj465,abn,abn,hj,ui}
{gh465,gh1,gh} => {gh,gh,gh}
{abcd,ab} => {ab,ab}

so... it's just a matter of truncating the number from the name? — Kevin Gosse, Oct 07 '16 at 06:31
Yes , but if the sequence is {a,a1,c34,b,b1} I need {a,a,c34,b,b} — user2630764, Oct 07 '16 at 06:33
@Manoz: I need it to be generic , the input is not static , sometimes it can be {c34} othertime {fg,fg56,jk} — user2630764, Oct 07 '16 at 06:37
A Linq query for this would be hard to read and inefficient. Better use a good old `foreach` loop with a `HashSet` to keep track of previously added items — Kevin Gosse, Oct 07 '16 at 06:40
@KooKiz _A Linq query for this would be hard to read and inefficient._ Please clarify. — Zev Spitz, Oct 07 '16 at 07:13
On what basis do you include `c34` as-is, but map `a1` to `a`? Please edit this information into your question. — Zev Spitz, Oct 07 '16 at 07:15
So `gh465`, `gh1` and `gh` would all map to `gh`. Would `gh465` map to `gh46` also? Or only `gh4651` maps to `gh465`? (Again, please edit this information into your question.) — Zev Spitz, Oct 07 '16 at 07:27
And what about pure letter sequences: `{"abcd", "ab"}` => `{"ab", "ab"}` ? (Your question doesn't describe all these details; please edit into the question.) — Zev Spitz, Oct 07 '16 at 07:32
@S.Akbari Because it's a string comparison based on other values. If this value starts with any other value, return that other value; otherwise return it as is. — Zev Spitz, Oct 07 '16 at 07:51
@ZevSpitz Hard to read because it's pretty much impossible to guess the intent just by reading the query. Inefficient because it's a solution of o(n²) complexity, where we could reach o(n log n) using a foreach loop with a HashSet — Kevin Gosse, Oct 07 '16 at 08:12

Zev Spitz · Accepted Answer · 2016-10-07T07:45:27.103

2

Since there are going to be no more than 5 strings at a time, efficiency is not a concern here.

var original = new List<string>() {"a","a1","c34","b","b1"};
var mapped = original.Select(x => original.Where(y => x.StartsWith(y)).Min()).ToList();

Note also that the comparison is case-sensitive; this can be fixed by passing in the appropriate StringComparison argument.

edited Oct 07 '16 at 07:45

answered Oct 07 '16 at 07:11

Zev Spitz

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Salah Akbari · Answer 2 · 2016-10-07T07:58:46.083

1

This code works for me:

var res = original.Select(c => c.Replace(c.Length == 2 ? c[1] : ' ', ' ')).ToList();

Input:

{ "a", "a1", "c34","a2", "b", "b1" } or {"a", "a1", "a2", "b", "b1"}

Output:

{ "a", "a", "c34","a", "b", "b" } or {"a", "a", "a", "b", "b"}

edited Oct 07 '16 at 07:58

answered Oct 07 '16 at 06:49

Salah Akbari

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You can use a multi-line lambda statement for clarity, as this question involves LINQ to Objects and `IEnumerable`, not `IQueryable`. – Zev Spitz Oct 07 '16 at 07:09
2

I guess this wouldn't work for the input (mentioned in the comments) of {fg,fg56,jk} ? – David_001 Oct 07 '16 at 07:10
@David_001 I think the behavior for `fg56` is like `c34` as OP mentioned in comments because he didn't said `fg56` should be mapped to `fg`! – Salah Akbari Oct 07 '16 at 07:14
Also, will this holds good for {test,test1,nothing} to {{test,test,nothing} as OP mentions it as dynamic – user1400915 Oct 07 '16 at 07:18
1

This is a good code, may need additional conditions like Alphabet check at a given index, based on use cases. Not possible to cover all undefined use cases +1 – Mrinal Kamboj Oct 07 '16 at 07:19
@user1400915 I've provided the answer based on the OP's expected output that mentioned in his/her original post and also comments. We can't provide a complete answer until he/she has a common pattern for mapping. For example are you sure `test1` should be `test`? because he/she didn't mentioned it explicitly. – Salah Akbari Oct 07 '16 at 07:23

Mapping list of items to shortest starting string in list

2 Answers2