How to get the Row Count of a specific column in UFT API

Question

I am using custom code in UFT API and need to get the row count of specific column.

A B

1 1

2 2

3 3

4

it can have different row count for each column and at a time i just need to read one column.

 var createlist = new List<string>();
 int rowno =GetDataSource("TACheck!Sheet1").RowsCount;
 for(int i=1;i<rowno;i++)
 {
   String val = GetDataSource("TACheck!Sheet1").GetValue(i,"A").ToString();
   createlist.Add(val);
 }