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;
}
}