Dear R Users,

Suppose I have a dataset like this:

  a       b

39700   485.00
39300   485.00
39100   480.00
38800   487.00
38800   492.00
39300   507.00
39500   493.00
39400   494.00
39500   494.00
39100   494.00
39200   490.00

Now I want get a-b for all possible combinations of a and b. Using two 'for'
loop it is easy to calculate. But problem arises when row length of the data
set is large eg. 1000 or more. Then R takes lot of time to do that. Can
anyone please tell me whether there is any R-function to do such kind of job
quickly?

Thanks and regards,

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