[R] Vertical subtraction in dataframes

[Gabor Grothendieck]

Try this ave solution noting that summing Count * (stain == "none")
over each group gives the Count in its stain=="none" row and ave
causes that Count value to be repeated for every row of the group so
we get a vector that can be subtracted from Count:

transform(DF, calib = Count - ave(Count * (stain == "none"), rep, FUN = sum))

and here is an SQL solution which works in roughly the same way:

library(sqldf)
sqldf("select rep, Count, stain, Count - none calib from DF
  natural join
  (select rep, sum(Count * (stain = 'none')) none from DF group by rep)")


On Fri, Mar 12, 2010 at 5:27 PM, Sam Albers <tonightsthenight at gmail.com> wrote:
> Hello all,
>
> I have not been able to find an answer to this problem. I feel like it might
> be so simple though that it might not get a response.
>
> Suppose I have a dataframe like the one I have copied below (minus the
> 'calib' column). I wish to create a column like calib where I am subtracting
> the 'Count' when 'stain' is 'none' from all other 'Count'  data for every
> value of 'rep'. This is sort of analogous to putting a $ in front of the
> number that identifies a cell in a spreadsheet environment.  Specifically I
> need some like this:
>
> mydataframe$calib <- Count - (Count when stain = none for each value rep)
>
> Any thoughts on how I might accomplish this?
>
> Thanks in advance.
>
> Sam
>
> Note: I've already calculated the calib column in gnumeric for clarity.
>
> rep Count stain calib
> 1 1522         none 0
> 1 147         syto -1375
> 1 544.8 sytolec -977.2
> 1 2432.6 sytolec 910.6
> 1 234.6 sytolec -1287.4
> 2 5699.8 none 0
> 2 265.6 syto -5434.2
> 2 329.6 sytolec -5370.2
> 2 383         sytolec -5316.8
> 2 968.8 sytolec -4731
> 3 2466.8 none 0
> 3 1303         syto -1163.8
> 3 1290.6 sytolec -1176.2
> 3 110.2 sytolec -2356.6
> 3 15086.8 sytolec 12620
>
> --
> *****************************************************
> Sam Albers
> Geography Program
> University of Northern British Columbia
> 3333 University Way
> Prince George, British Columbia
> Canada, V2N 4Z9
> phone: 250 960-6777
> *****************************************************
>
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