c# comparing arrays

Question

good afternoon everybody

the question is kinda simple but I've been having problems the whole afternoon

i have 2 lists:

list of ints (ids)
list of objects (that contains ids)

and i want to compare them but i want to obtain the id that doesn't have a pair (if it exists)

i was wondering if there's a c# or linq method to identify the values that are different in two arrays

example

if i have

List<int> ids = {1,2,3,4,5}

and

List<objectX> x = (contains id,code, and description)

and i was trying something like

foreach (int id in ids)
        {
            foreach (objectX item in x)
            {
                if (item.id == id)
                {
                    break;
                }
                else
                    idDiferentes.Add(id);
            }
        }

but like you can imagine it doesn't work

for example

ids= {1,2,3,4}
objectx[id] ={1,3,2}

the ids are different when i compare them so i get a bigger list that the one i need

i also tried with an linq outer join but i don't understand how it works pretty well

if (item.id != id) idDiferentes.Add(id), and please don't use "u" instead of "you" and "i" instead of "I". — khachik
– khachik, Commented May 20, 2011 at 20:05

Anthony Pegram · Accepted Answer · 2011-05-20 20:04:50Z

10

var idsWithoutObjects = ids.Except(x.Select(item => item.id));

answered May 20, 2011 at 20:04

Anthony Pegram

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Comments

Rune Grimstad · Accepted Answer · 2011-05-20 20:05:23Z

7

What you are after is the Except extension method. It gives you the set difference between two sequences.

So you can do something like this (pseudo c#-code):

var idDifferences = x.Select(item => item.id).Except(ids);

answered May 20, 2011 at 20:05

Rune Grimstad

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Comments

Nicholas Carey · Accepted Answer · 2011-05-20 20:12:03Z

3

Linq Set Operations:

int[] A = { 1 , 2 , 3 , 4 , 5 ,     } ;
int[] B = {     2 , 3 , 4 , 5 , 6 , } ;

int[] A_NotIn_B = A.Except( B ).ToArray() ;
int[] B_NotIn_A = B.Except( A ).ToArray() ;

There you go.

answered May 20, 2011 at 20:12

Nicholas Carey

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Comments

WildCrustacean · Accepted Answer · 2011-05-20 20:13:07Z

1

As an alternative to LINQ (although LINQ is probably the right answer here), if all your ids are unique you may be able to use the Contains() method, for example:

foreach(objectX item in x)
{
    if(!ids.Contains(item.id))
    {
        idDiferentes.Add(item.id);
    }
}

edited May 20, 2011 at 20:13

answered May 20, 2011 at 20:06

WildCrustacean

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Comments

Philip Sheard · Accepted Answer · 2011-05-20 20:09:30Z

0

It is easier to use a flag, e.g.:

bool b = False;

foreach (int id in ids)
        {
            foreach (objectX item in x)
            {
                if (item.id == id)
                {
                    b = True;
                    break;
                }
            }
        }

if (!b)
{
    idDiferentes.Add(id);
}

answered May 20, 2011 at 20:09

Philip Sheard

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2 Comments

Anthony Pegram Over a year ago

this would not compile. Among other issues, you have the if (!b) outside of the outer foreach, and id is no longer in scope.

Carlos Guillermo Bolaños Lopez Over a year ago

Excelent Guys Thank you very much for your help, thanks to you i could solve my problem

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