Hello, I'm trying to extract the common rows from a data frame, which is
something like this :


*   DEPTH SALINITY DEPTH SALINITY*
*18    87    39.06    94    39.06*
*19   173    39.05   141       NA*
*20   260    39.00   188    39.07*
*21   312    38.97   207    39.03*
*22     1    39.36     1    39.35*
*23    10    39.36    10    39.33*
*24    20    39.36    20    39.33*
*25    30    39.35    30    39.33*
*
*
i want to extract the rows with the same depth.
i cannot do something like *data.frame[22:25,]* because i have lots of rows

any help?
thank you

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