[R] Calculating rowMeans from different columns in each row?

[Phil Spector]

Marine -
    Assuming your data frame is named "df", I think

apply(df,1,function(x)mean(x[x[7]:x[8]]))

will give you what you're looking for.
 					- Phil Spector
 					 Statistical Computing Facility
 					 Department of Statistics
 					 UC Berkeley
 					 spector at stat.berkeley.edu


On Thu, 10 Feb 2011, Marine Andersson wrote:

> Hello!
>
> I have a dataset like this:
>
> X1   X2   X3   X4   X5    X6    X7    X8
> 1     2      2     1     2      3       2      6
> 2     3      2     5     7      9       1      3
> 1    9     12     6     1      1       3      6
>
> The columns X1-X6 contains ordinary numeric values.
>
> X7 contains the number of the first column that the rowMeans should be calculated from and
> X8 contains the last column that should be included in the rowMeans.
>
> when I try
>
> test <- (df[,df$X7:df$X8])
>
> the rowMeans are calculated based on the values in the X7 and X8 in the first row only.
>
> Thanks in advance!
>
> /Marine
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