Linux file sort with incomplete columns -

i need sort file first column, if there numerical entry, , second column when there none in first. looks this:

3 - foo bar 1 1 foo bar - 5 foo bar 2 2 foo bar - 4 foo bar 

and need output be

1 1 foo bar 2 2 foo bar 3 - foo bar - 4 foo bar - 5 foo bar 

is there nice way in linux single command? thanks!

on output follows format can use basic sort command:

sort -k 1,2 foo.txt