Let say I have an array like this.
int[] arr = {1,2,3,4,4,5,6,7,8,8,8,1};
How do I shuffle it, but have all equal values beside each other?
Sample expected output after shuffle:
3,1,1,8,8,8,7,2,4,4,6,5
2 Answers
You can do something like this:
- Find the unique values in the array and the number of times each one occurs. Store the counts in a dictionary, say
counts. - Shuffle the unique values using a shuffling algorithm such as Fisher-Yates.
- For each value
vin the shuffled array, writevinto the output arraycounts[v]times.
Comments
var rng = new Random();
arr = arr
.GroupBy(i => i)
.OrderBy(g => rnd.Next())
.SelectMany(g => g)
.ToArray();
7 Comments
ProgrammingLlama
What is
rnd (please edit your code to show this)? Please provide more details about how your answer works. I agree that this is likely the neatest way to solve this problem (although not using the shuffling algorithm OP asked for), but OP/future readers may require a little more of an explanation.
JosephDaSilva
This works only if the
g => rnd.Next() function is guaranteed to be called only once per group element. While this is true (at least in .NET 5), this solution is relying on undocumented behavior.JosephDaSilva
In general when using LINQ you should not rely on how many calls will be made to your lambda functions, or which arguments they will be called with, or in what order the calls will be made. See this: github.com/dotnet/runtime/issues/31554
ProgrammingLlama
@JosephDaSilva Why does it only work if it's only guaranteed to be called once per group element? What issues do you see if it's called more than once?
JosephDaSilva
@Llama If the key selector is called more than once and returns a different random value each time then you have an inconsistent comparison function (for example, it may report
x < y when called once and x > y when called a second time). Some sorting algorithms may throw errors or go into infinite loops when given inconsistent comparison functions. ericlippert.com/2011/01/31/bad-comparisons-part-four |
{1, 1, 2, 2, 1, 1, 2, 2}? If so, is{2, 2, 1, 1, 2, 2, 1, 1}a valid output? Or are{1, 1, 1, 1, 2, 2, 2, 2}and{2, 2, 2, 2, 1, 1, 1, 1}the only valid outputs?