R help - Apr 2012 - Using if and else in a data frame

Dear list,
I get the ifelse function to work on a data frame but don't know how to do
something similar (only more conditions) with the combination of if and else
like in the example:

 A <-
c("a","a","b","b","c","c")
 B <- c(rep(2,6))
 dat <- data.frame(A,B)
 dat$C <- if(AB$A=="a") {AB$B^2} else
          if(AB$A=="b") {AB$B+5} else
          if(AB$A=="c") {AB$B}

So I have a data frame (e.g. "dat") and want to create an new column
for
that data frame applying certain conditions depending on the values of the
other columns of the data frame.

In this case I would like R to create a column with the following variables:
4,4,7,7,2,2. So if column A has the value "a" then do value of column
B^2,
but if the value is "b" then do B-value + 5, and finally if the value
in
column A is "c", then just copy the value of column B.

Hope someone can help... and thanx a lot!

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Hello,

Your example code has a bug, there's no fata.frame called 'AB'.
It's
corrected below.


pannigh wrote
> 
> Dear list,
> I get the ifelse function to work on a data frame but don't know how to
do
> something similar (only more conditions) with the combination of if and
> else like in the example:
> 
>  A <-
c("a","a","b","b","c","c")
>  B <- c(rep(2,6))
>  dat <- data.frame(A,B)
>  dat$C <- if(AB$A=="a") {AB$B^2} else
>           if(AB$A=="b") {AB$B+5} else
>           if(AB$A=="c") {AB$B}
> 
> So I have a data frame (e.g. "dat") and want to create an new
column for
> that data frame applying certain conditions depending on the values of the
> other columns of the data frame.
> 
> In this case I would like R to create a column with the following
> variables: 4,4,7,7,2,2. So if column A has the value "a" then do
value of
> column B^2, but if the value is "b" then do B-value + 5, and
finally if
> the value in column A is "c", then just copy the value of column
B.
> 
> Hope someone can help... and thanx a lot!
> 
Now, let's run it.


A <-
c("a","a","b","b","c","c")
B <- c(rep(2,6))
dat <- data.frame(A,B)
dat$C <- if(dat$A=="a"){dat$B^2} else
          if(dat$A=="b") {dat$B+5} else
          if(dat$A=="c") {dat$B}
Warning message:
In if (dat$A == "a") { :
  the condition has length > 1 and only the first element will be used

'ifelse' is vectorized, 'if / else' is not. The condition does
have length >
1:

dat$A=="a"
[1]  TRUE  TRUE FALSE FALSE FALSE FALSE

Length 6, only the first, TRUE, is used and dat$C <- dat$B^2.

The solution is to use 'ifelse'.

dat <- data.frame(A,B)
dat$C <- ifelse(dat$A == "a", dat$B^2,
           ifelse(dat$A == "b", dat$B + 5, dat$B))

Hope this helps.

Rui Barradas



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