If condition statment within function in R - r

Question

I have one question which is probably easy for a lot of you. I would like to write a function which will do the calculations based on condition in selected column. It will be easier to show you an example:
con <- c("A", "B", "B", "C", "C", "A", "D", "A", "B", "D", "D", "D")
value <- c(1, 3, 2, 1, 1, 1, 2, 1, 2, 3, 3, 2)
dat <- data.frame(con, value)
head(dat)
So one possibility would be to do this in this simple way:
dat$new <- ifelse(dat$con == "A", dat$value*10,
ifelse(dat$con == "B", dat$value*100, dat$value*1000))
head(dat)
But, my question is how would the function look like? I tried something like this, but it is not working. Can someone help me with explanation what is missing and wrong?
calc <- function(dat) {
if(dat[, con] == "A") {
new <- dat$value*10
}
if(dat[, con] == "B") {
new <- dat$value*100
} else {
new <- dat$value*1000
}
}
calc(dat)

Answer 1

You can also create a function without if and ifelse:
calc <- function(data)
transform(data, new = value * 1000 / 100 ^ (con == "A") / 10 ^ (con == "B"))
The function is based on mathematical operations.
calc(dat)
# con value new
# 1 A 1 10
# 2 B 3 300
# 3 B 2 200
# 4 C 1 1000
# 5 C 1 1000
# 6 A 1 10
# 7 D 2 2000
# 8 A 1 10
# 9 B 2 200
# 10 D 3 3000
# 11 D 3 3000
# 12 D 2 2000

Answer 2

calc <- function(dat) {
dat$new <- ifelse(dat[,'con'] == 'A', dat[,'value']*10,
ifelse(dat[,'con'] == 'B', dat[,'value']*100,
dat[,'value']*1000)
)
dat
}
The subsetting operator $ is problematic in functions. Instead using the framework DF[,'<variable>'] is better. Also, note the quotation marks around the variable names (column names). Also your original function does not print a result to the screen. The last command will be returned when the function is called.
calc(dat)
con value new
1 A 1 10
2 B 3 300
3 B 2 200
4 C 1 1000
5 C 1 1000
6 A 1 10
7 D 2 2000
8 A 1 10
9 B 2 200
10 D 3 3000
11 D 3 3000
12 D 2 2000