What is a "variable"? LabVIEW does not distiguish between row and column arrays. They are both 1D arrays. A matrix is a special datatype. Typically we deal with 2D arrays instead.
If you want to form a 2D array, you should make sure that all calls to the while loop result in the same number of column elements (maybe a FOR loop would be better?). LabVIEW does not directly support ragged arrays (you could use an array of clusters of a 1D array, for example.
Please show us your code so we get s better idea of what you are asking.