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rdataframeoperation

Subtracting small data.frame from large data.frame by grouped a variable

I have got a very large data set

  mdf <- data.frame (sn = 1:40, var = rep(1:10, 4), block = rep(1:4, each = 10), 
yld = c(1:40))

I have small data set 

blockdf <- data.frame(block = 1:4, yld = c(10, 20, 30, 40)) # block means

All variables in both dataset except yld are factors.

I want to subtract block means (blockdf$yld) form each mdf$yld dataset, such that the block effects should correspond to block in mdf dataframe.

for example: value 10 will be substracted from all var within 
   first block yld in mdf 
                   20  -  second block yld in mdf

and so on

Please note that I might have sometime unbalance number of var within the reps. So I want to write it in such way that it can handle unbalance situation

Solution

  • This should do the trick

    block_match <- match(mdf$block, blockdf$block)
transform(mdf, yld = yld - blockdf[block_match, 'yld'])