Randomizing rows in a DataTable

I've been working on a project recently where I had the need to randomly shuffle all of the rows in a DataTable. I wanted to do it with the DataTable itself instead of in the act of populating the DataTable for a couple of reasons: 1) I wanted to keep the DataTable in memory and shuffle it in place multiple times without going back to the source, and 2) I had multiple sources where data was coming from (SQL and XML) so I preferred to keep the randomization logic in one place. I also didn't want to copy all of the data (even though it was not a large amount) each time I shuffled, so I decided to use a DataView to display the data shuffled each time I needed it.

Here's the utility function I came up with - each time you call RandomizeDataTable it will return a newly shuffled DataView of all the data passed in through the DataTable. Note that because I reuse the added column "rndSortId" each time, any DataViews retrieved from previous calls to the method will have the new shuffle order. You could change this behavior by adding a new column each time with its own unique sort sequence.

As always, comments/improvements welcome – enjoy!

public static class DataSetUtilities

{

static Random _rand = new Random();

public static DataView RandomizeDataTable(DataTable dt)

{

// Create array of indices and populate with ordinal values

int[] indices = new int[dt.Rows.Count];

for (int i = 0; i < indices.Length; i++)

indices[i] = i;

// Knuth-Fisher-Yates shuffle indices randomly

for (int i = indices.Length - 1; i > 0; i--)

{

int n = _rand.Next(i + 1);

int tmp = indices[i];

indices[i] = indices[n];

indices[n] = tmp;

}

// Add new column to data table (if it's not there already)

// to store shuffle index

if (dt.Columns["rndSortId"] == null)

dt.Columns.Add(new DataColumn("rndSortId", typeof(int)));

int rndSortColIdx = dt.Columns["rndSortId"].Ordinal;

for (int i = 0; i < dt.Rows.Count; i++)

dt.Rows[i][rndSortColIdx] = indices[i];

DataView dv = new DataView(dt);

dv.Sort = "rndSortId";

return dv;

}

}