Read the data file into an one-dimentional array in C#

I have a text file including some "double data" with a "large number of lines (e.g 20000 lines)" and "small number of columns (eg 6 columns)" in which the last line has a smaller number of columns for example:
1   2   3   4   5   6
7  8   9   10  11  12
13  14  15  16  17  18
.
.
.

1  2.1  3.1
How can I read this data file and put it in "one dimentional array"?

Thanks alot