I need to combine multiple columns into a single column, so:

one     four    seven
two     five    eight
three   six     nine

Becomes:

one
two
three
four
five
six
seven
eight
nine
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That's not possible with plain old formula's. Have a look at this answer: webapps.stackexchange.com/a/39292/29140 –  Jacob Jan Tuinstra Jun 4 '13 at 12:27
–  batpigandme Jun 4 '13 at 12:49
@JacobJanTuinstra Unfortunately that merges sheets, not columns. –  1ndivisible Jun 4 '13 at 12:53
It works for column ranges as well. –  Jacob Jan Tuinstra Jun 4 '13 at 13:02
@JacobJanTuinstra since the answer to this and the other thread I cited above are the same should they be considered duplicates? (Great script find BTW) –  batpigandme Jun 4 '13 at 13:18

Install the VMERGE script from the script gallery:

The script you just installed, makes it possible to combine multiple ranges into one: =VMERGE(range1,range2, ect)

See example file I've prepared for you to play with: VMERGE and Ranges

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Beautiful. Much obliged. –  1ndivisible Jun 4 '13 at 13:57
At this time the Script Gallery is available only for old spreadsheets that had not being migrated yet. –  Rubén May 3 at 0:44
Yeah; no more VMERGE still. –  Jason C Jul 18 at 9:13

The following formula can be used to merge one column after another:

={A1:A5; M1:M5}
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+1 The principle works well for me, though something like ={A1:A3;B1:B3;C1:C3} might have been more in keeping with the OP. –  pnuts Oct 14 '14 at 19:04

You can try this function to combine two columns

=unique(transpose(split(join(";",A:A)&join(";",B:B),";")))