Question

I have what seems to be a simple problem but I can’t figure it out so far.

Say I have two arrays:

int[] values = {10,20,20,10,30};
int[] keys = {1,2,3,4,5};

Array.Sort(values,keys);

Then the arrays would look like this:

values = {10,10,20,20,30};
keys = {4,1,2,3,5};

Now, what I want to do is make it so that the keys are also sorted in second priority so the key array to look like this:

keys = {1,4,2,3,5};

Notice the 1 and 4 values are switched and the order of the value array has not changed.

Answer 1

If an “in-place sorting” is not strictly necessary for you, I suggest to use OrderBy:

var sortedPairs = values.Select((x, i) => new { Value = x, Key = keys[i] })
                        .OrderBy(x => x.Value)
                        .ThenBy(x => x.Key)
                        .ToArray(); // this avoids sorting 2 times...
int[] sortedValues = sortedPairs.Select(x => x.Value).ToArray();
int[] sortedKeys = sortedPairs.Select(x => x.Key).ToArray();

// Result:
// sortedValues = {10,10,20,20,30};
// sortedKeys = {1,4,2,3,5};