[R] making operators act on rows of a data frame

[Petr Pikal]

   Hi

   On 11 Mar 2004 at 12:13, Jonathan Williams wrote:

   > Dear R helpers,

   > I wish to use the "sum" operator for each row of a data frame.

   > However, it appears that the operator acts on the entire data

   > frame, over all columns. What is the best way to obtain row-

   > wise operation?

   >

   > The following code shows my attempts so far, and their problems:-

   >

   > test1=array(rbinom(120,1,0.5),c(20,3))

   > test1[,3]=NA

   > sum(test1[,1:2])

   Try rowSums()

   rowSums(test1, na.rm=T)

   > test1[,3][sum(test1[,1:2])>=2]=1

   > test1[,3][sum(test1[,1:2])]

   > test1

   >

   > test2=array(rbinom(120,1,0.5),c(20,3))

   > test2[,3]=NA

   This can be done by

   test2[rowSums(test2, na.rm=T)>=2,3]<-1

   Cheers

   Petr

   > sum(test2[,1:2])

   > test2[,3][(test2[,1]+test2[,2])>=2]=1

   > test2[,3][sum(test2[,1:2])]

   > test2

   >

   > In the 1st section, I try to use "sum" to add the first two columns
   of

   > a data frame. Here, sum(test1[,1:2]) evaluates to a single integer
   but

   > this modifies *all* the rows of test1.

   >

   > In the 2nd section, specifying addition of the first two columns
   with

   > a '+' acts row-by row, as I want. This is OK for this demonstration,

   > but would be impractical in the program I am trying to write (where

   > the columns I wish to sum are numerous and change from time to
   time).

   >

   > I would be very grateful to know if it is possible to get operators
   to

   > act on rows of a data frame, and if so, how.

   >

   > I am running R1.8.1 on Windows NT.

   >

   > Jonathan Williams

   > OPTIMA

   > Radcliffe Infirmary

   > Woodstock Road

   > OXFORD OX2 6HE

   > Tel +1865 (2)24356

   >

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   Petr Pikal

   petr.pikal at precheza.cz