[R] (no subject)

[Aimin Yan]

I have a data set like this:
if I want to less than 200000 obs from this data set.
How can I do these?

 > str(p1982)
'data.frame':   465979 obs. of  6 variables:
  $ p  : Factor w/ 1982 levels "154l_aa","1A0P_aa",..: 1 1 1 1 1 1 1 1 1 1 ...
  $ aa : Factor w/ 19 levels "ALA","ARG","ASN",..: 2 16 4 5 18 3 19 3 2 9 ...
  $ as : num  152.0  15.9  65.1  57.2  28.9 ...
  $ ms : num  108.8  28.3  59.2  49.9  31.8 ...
  $ cur: num  -0.1020  0.2564  0.0312 -0.0550  0.0526 ...
  $ sc : num   92.10 103.67   7.27  72.98  96.12 ...