I have some spreadsheet data which I want to present in columns, instead of the rows that I initially entered. I searched a bit and found instructions for Excel here. The principle is the same, so here’s what I did for Gnumeric.
First, select and copy the cells you want. Then, open a new sheet, right click and select Paste Special from the menu. A popup window will appear with several options. From the Region Operation, select Transpose: