Hello:
How can I interchange symbols for numeric values in a data frame.

> test
  f  s  t
1 a  1 -1
2 b  1 -3
3 c -1  1

say I have test d.f . I want to make flip number that are positive to
negative and negative to positive only for numerics in column 's'

my desired result:

> new.test
  f  s  t
1 a  -1 -1
2 b  -1 -3
3 c  1  1


thanks
Adrian

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