[R] replace numbers in a column conditional on their value

[Richard.Cotton at hsl.gov.uk]

>   I have a data frame column in which I would like to replace some 
> of the numbers dependent on their value.
> 
>   data frame = zz
> 
>   AveExpr         t      P.Value       FC
> 7.481964  7.323950 1.778503e-04 2.218760
> 7.585783 12.233056 6.679776e-06 2.155867
> 6.953215  6.996525 2.353705e-04 1.685733
> 7.647513  8.099859 9.512639e-05 1.674742
> 7.285446  7.558675 1.463732e-04 1.584071
> 6.405605  3.344031 1.276812e-02 1.541569
> 
>   I would like to replace the values in column 'FC' which are >2 
> with their squared value.
>   If I do this, however, I get a warning but it does the sum correctly.
>   Warning message:
> number of items to replace is not a multiple of replacement length 
> in: zz[, 4][zz[, 4] > 2] <- zz[, 4]^2 

Try
zz$FC[zz$FC > 2] <- (zz$FC[zz$FC > 2])^2

Regards,
Richie.

Mathematical Sciences Unit
HSL


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