# Re: [R] recoding one variable into another - but differently for different cases

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Tue, 22 Jan 2008 14:08:47 -0500

You could create a lookup table or use recode in the car package.

Another possibility is to use a logical/arithmetic expression. The following expression says that

• if A is 1 then use the first term equals the coefficient, namely 1 if B ==1 and -1 if B == 2. Also, if A is not 1 then that term is zero and can be ignored.
• if A is 2 or 99 then the second or third terms are used analogously
• otherwise no terms are selected and the expression equals zero

transform(Data, new =

(A == 1) * ((B == 1) - (B == 2)) + (A == 2) * ((B == 2) - (B == 1)) + (A == 4) * 99)

This could be reduced even more although at the expense of understandability, e.g.

transform(Data, new = ifelse(A > 2, 99 * (A == 4), (A == B) - (A != B)))

On Jan 22, 2008 12:25 PM, Dimitri Liakhovitski <ld7631_at_gmail.com> wrote:
> Hello,
> I have 2 variables in my sample Data: Data\$A and Data\$B
> Variable Data\$A can assume values: 1, 2, 3, and 4.
> Variable Data\$B identifies my cases and can assume values: 1 and 2.
>
> I need to recode my variable Data\$A into a new variable Data\$new such that:
>
> People who are Data[Data\$B %in% 1, ] are recoded like this:
>
> Value on Data\$A Value on Data\$new
> 1 +1
> 2 -1
> 3 0
> 4 99
>
> People who are Data[Data\$B %in% 2, ] are recoded like this:
>
> Value on Data\$A Value on Data\$new
> 1 -1
> 2 +1
> 3 0
> 4 99
>
> I am having hard time doing this. Any help would be greatly appreciated.
> Dimitri
>
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