Calculating difference between values in data frame based on separate column
Here's another way, using the reshape2 package: library(reshape2) d <- dcast(df, vial ~ measure, value_var = 'value') d$diff <- with(d, B - A)
d
vial A B diff 1 1 12 26 14 2 2 30 45 15 3 3 27 32 5 4 4 6 34 28 HTH, Dennis
On Fri, Oct 21, 2011 at 3:31 PM, Nathan Miller <natemiller77 at gmail.com> wrote:
Hi all, Say I have a data frame something like the one below with different sample vials, measured before(B) and after(A) some process, with a value recorded at each measurement point vial ? ?measure ? ?value 1 ? ? ? B ? ? ? ? ? ? ? ?26 1 ? ? ? A ? ? ? ? ? ? ? ?12 2 ? ? ? B ? ? ? ? ? ? ? ? 45 2 ? ? ? A ? ? ? ? ? ? ? ? 30 3 ? ? ? B ? ? ? ? ? ? ? ? 32 3 ? ? ? A ? ? ? ? ? ? ? ? 27 4 ? ? ? B ? ? ? ? ? ? ? ? 34 4 ? ? ? A ? ? ? ? ? ? ? ? 6 Is there an easy means by which I can subtract the after (A) measurements from the before (B) measurement for each vial in this data frame so I am left with a data frame that contains the vial number and difference between A and B? I've played around with writing a function and applying it with ddply, but haven't stumbled on a technique that works, though I feel there should be something simple means of doing this that I'm just not seeing. Thanks for you help, Nate ? ? ? ?[[alternative HTML version deleted]]
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