They have to be in linear sections, or you have to get creative with formulas or such.  Or if just that weird and discontiguous, manually grabbing bits with old cut/paste and a mouse click.

You'll want to learn to use at least basic (and not so basic) formulas if you are at that point.  I use calc a _lot_, sadly spreadsheets are the lowest common denominator most enterprises understand, but I deal with some rather large data sets at time I need to pick and choose from, akin to your "multiple selection" analogy to create some unique resultant data set, and so I have to use formula's to match cells in some way, form the data with a concatenate, and then produce a single cell of the resultant output.  Similar to programmatically formulating your resultant output in any data set.

This can be a whole class in itself on how to use formulas in excel/calc (and usually is), but no time like the present to learn if you work with it often enough like I do.

-mb