[R] Subtracting elements of data.frame

[Peter Ehlers]

On 2011-01-25 01:20, Vincy Pyne wrote:
> Dear R helpers
>
> I have a dataframe as
>
> df = data.frame(x = c(1, 14, 3, 21, 11), y = c(102, 500, 40, 101, 189))
>
>> df
>     x   y
> 1  1 102
> 2 14 500
> 3  3  40
> 4 21 101
> 5 11 189
>
> # Actually I am having dataframe having multiple columns. I am just giving an example.
>
> I need to subtract all the rows of df by the first row of df i.e. I need to subtract each element of 'x' column by 1. Likewise I need to subtract all elements of column 'y' by 11. Thus I need an output like
>
>> df_new
>     x   y
> 1  0   0
> 2 13 398
> 3  2 -62
> 4 20  -1
> 5 10  87
>
> As I had mentioned above, I have number of columns in reality and thus I can't use the command
>   say
>
> df_new = data.frame(x = df$x-df$x[1], y = df$y-df$y[1])
>
> Kindly guide

You've already had good simple solutions. Here's one more,
using the plyr package:

  require(plyr)
  df_new <- colwise(.fun = function(x) {x - x[1]})(df)

plyr is very handy for all sorts of data manipulations.

Peter Ehlers

>
> Thanking you all in advance
>
> Regards
>
> Vincy
>
>
>
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