[R] conditional selection of dataframe rows

[David Winsemius]

On Aug 12, 2010, at 3:11 PM, Toby Gass wrote:

> Dear helpeRs,
>
> I have a dataframe (14947 x 27) containing measurements collected
> every 5 seconds at several different sampling locations.  If one
> measurement at a given location is less than zero on a given day, I
> would like to delete all measurements from that location on that day.
>
> Here is a toy example:
>
> toy <- data.frame(CH = rep(3:5,3), DAY = c(rep(4,5), rep(5,4)),
> SLOPE = c(seq(0.2,0.6, .1),seq(0.2, -0.1, -0.1)))
>
> In this example, row 9 has a negative measurement for Chamber 5, so I
> would like to delete row 6, which is the same Chamber on the same
> day, but not row 3, which is the same chamber on a different day.  In
> the full dataframe, there are, of course, many more days.
>
> Is there a handy R way to do this?

toy[ - which(toy$SLOPE <0 ) , ]

>
> Thank you for the assistance.
>
> Toby
>
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David Winsemius, MD
West Hartford, CT