CODEWITHSUNDEEP
c#arrayslinq
dursk
dursk

Reputation: 4445

LINQ search though a list of string arrays for a particular string

I have a list of string arrays:

List<String[]> listOfStringArrays = something;

I need to select all objects from a collection that have a value which is equal to the string at the 0th index of any string array in the list.

For example, if I just had a simple list of strings, declared as:

List<String> listOfStrings = something;

I would just do:

var query = someCollection.Where(x => listOfStrings.Contains(x.id_num))

But obviously it's not as simple with a list of string arrays.

I know that I can easily just iterate through the list of string arrays and create a simple list of strings with the 0th value, like this:

List<String[]> listOfStringArrays = something;
List<String> listOfValues = new List<String>();

foreach (string[] s in listOfStringArrays)
    listOfValues.Add(s[0]);

var query = someCollection.Where(x => listOfValues.Contains(x => x.id_num);

But would really like to avoid this and am trying to write it as a one liner without introducing extra lists and loops.

Upvotes: 7

Views: 40033

Answers (4)

MarcinJuraszek
MarcinJuraszek

Reputation: 125630

You can put it all into one query:

someCollection.Where(x => listOfValues.Select(y => y[0]).Contains(x => x.id_num);

But it will iterate over listOfValues over and over again.

I would rather go with HashSet<string> to make it faster:

var set = new HashSet<string>(listOfValues.Select(y => y[0]));
someCollection.Where(x => set.Contains(x));

Upvotes: 11

Daniel C
Daniel C

Reputation: 1362

It should be simply:

List<String[]> newListOfStrings = listOfStrings.where(x => x[0].Contains(identifer)).ToList()

The final ToList is needed in this case because I have not used var.

Upvotes: 1

JaredPar
JaredPar

Reputation: 754725

Try the following

var query = someCollection.Where(s => listOfStringArrays.Any(a => a[0] == s));

Upvotes: 3

Jean-Bernard Pellerin
Jean-Bernard Pellerin

Reputation: 12670

var firsts = listOfString.Select(x => x[0]);
var query = someCollection.Where(x => firsts.Contains(x));

This will project each array to it's first element, and then match from there

As a one liner:

var query = someCollection.Where(x => listOfString.Select(y => y[0]).Contains(x));

Upvotes: 1

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