Selecting strings and using in logical expressions to create new variable - R - r

Question

I have a categorical variable indicating location of flu clinics as well as an "other" category. Participants who select the "other" category give open-ended responses for their location. In most cases, these open-ended responses fit with one of the existing categories (for example, one category is "public health clinic", but some respondents picked "other" and cited "mall" which was a public health clinic). I could easily do this by hand but want to learn the code to select "mall" strings then use logical expressions to assign these people to "public health clinic" (e.g. create a new variable for location of flu clinics).
My categorical variable is "lrecflu2" and my character string variable is "lfother"
So far I have:
mall <- grep("MALL", Motiv82012$lfother, value = TRUE)
This gives me a vector with all the string responses containing "MALL" (all strings are in caps in the dataframe)
How do I use this vector in a logical expression to create a new variable that assigns these people to the "public health clinic" category and assigns the original value of flu clinic location variable for people that did not select "other" (and do not have values in the character string variable) to the new flu clinic location variable?
Perhaps, grep is not even the right function to be using.

Answer 1

As I understand it, you have a column in a data frame, where you want to reassign one character value to another. If so, you were almost there...
set.seed(1) # for generating an example
df1 <- data.frame(flu2=sample(c("MALL","other","PHC"),size=10,replace=TRUE))
df1$flu2[grep("MALL",df1$flu2)] <- "PHC"
Here grep() is giving you the required vector index; you then subset the vector based on this and change those elements.
Update 2
This should produce a data.frame similar to the one you are using:
set.seed(1)
lreflu2 <- sample(c("PHC","Med","Work","other"),size=10,replace=TRUE)
Ifother <- rep("",10) # blank character vector
s1 <- c("Frontenac Mall","Kingston Mall","notMALL")
Ifother[lreflu2=="other"] <- s1
df1 <- data.frame(lreflu2,Ifother)
### alternative:
### df1 <- data.frame(lreflu2,Ifother, stringsAsFactors = FALSE)
df1
gives:
lreflu2 Ifother
1 Med
2 Med
3 Work
4 other Frontenac Mall
5 PHC
6 other Kingston Mall
7 other notMALL
8 Work
9 Work
10 PHC
If you're looking for an exact string match you don't need grep at all:
df1$lreflu2[df1$Ifother=="MALL"] <- "PHC"
Using a regex:
df1$lreflu2[grep("Mall",df1$Ifother)] <- "PHC"
gives:
lreflu2 Ifother
1 Med
2 Med
3 Work
4 PHC Frontenac Mall
5 PHC
6 PHC Kingston Mall
7 other notMALL
8 Work
9 Work
10 PHC
Whether Ifother is a factor or vector with mode character doesn't affect things. data.frame will coerce string vectors to factors by default.