[R] How to add a variable to a dataframe whose values are conditional upon the values of an existing variable

[Daniel Malter]

Hi, two approaches at least.

a. a nested ifelse statement
b. merging the original data frame with DOW in it with a data frame that
holds the day "MON" to "SUN" and their indicators.

Both approaches illustrated below:

DOW=rep(c("MON","TUE"),100)

#nested ifelse approach
DOW.ind=ifelse(DOW=="MON",1,ifelse(DOW=="TUE",2,0)) 
#continue to nest ifelse statements for more days

DOW.ind

#merging approach
day=c("MON","TUE") 
ind=c(1,2)
ind.frame=data.frame(day,ind)
merge(data.frame(DOW),ind.frame,by.x="DOW",by.y="day",all.x=T,all.y=F)

HTH,
Daniel

-------------------------
cuncta stricte discussurus
-------------------------
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Steve Matco
Sent: Friday, February 26, 2010 2:32 PM
To: r-help at r-project.org
Subject: [R] How to add a variable to a dataframe whose values are
conditional upon the values of an existing variable

Hi everyone,

I am at my wits end with what I believe would be considered simple by a more
experienced R user. I want to know how to add a variable to a dataframe
whose values are conditional on the values of an existing variable. I can't
seem to make an ifelse statement work for my situation. The existing
variable in my dataframe is a character variable named DOW which contains
abbreviated day names (SAT, SUN, MON.....FRI). I want to add a numerical
variable named DOW1 to my dataframe that will take on the value 1 if DOW
equals "SAT", 2 if DOW equals "SUN", 3 if DOW equals "MON",.....,7 if DOW
equals "FRI". 
I  know this must be a simple problem but I have searched everywhere and
tried everything I could think of. Any help would be greatly appreciated.

Thank you,

Mike




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