How can I strip dollar signs ($) from a data frame in R? - r

Question

I'm quite new to R and am battling a bit with what would appear to be an extremely simple query.
I've imported a csv file into R using read.csv and am trying to remove the dollar signs ($) prior to tidying the data and further analysis (the dollar signs are playing havoc with charting).
I've been trying without luck to strip the $ using dplyr and gsub from the data frame and I'd really appreciate some advice about how to go about it.
My data frame looks like this:
> str(data)
'data.frame': 50 obs. of 17 variables:
$ Year : int 1 2 3 4 5 6 7 8 9 10 ...
$ Prog.Cost : Factor w/ 2 levels "-$3,333","$0": 1 2 2 2 2 2 2 2 2 2 ...
$ Total.Benefits : Factor w/ 44 levels "$2,155","$2,418",..: 25 5 7 11 12 10 9 14 13 8 ...
$ Net.Cash.Flow : Factor w/ 45 levels "-$2,825","$2,155",..: 1 6 8 12 13 11 10 15 14 9 ...
$ Participant : Factor w/ 46 levels "$0","$109","$123",..: 1 1 1 45 46 2 3 4 5 6 ...
$ Taxpayer : Factor w/ 48 levels "$113","$114",..: 19 32 35 37 38 40 41 45 48 47 ...
$ Others : Factor w/ 47 levels "-$9","$1,026",..: 12 25 26 24 23 11 9 10 8 7 ...
$ Indirect : Factor w/ 42 levels "-$1,626","-$2",..: 1 6 10 18 22 24 28 33 36 35 ...
$ Crime : Factor w/ 35 levels "$0","$1","$10",..: 6 11 13 19 21 23 28 31 33 32 ...
$ Child.Welfare : Factor w/ 1 level "$0": 1 1 1 1 1 1 1 1 1 1 ...
$ Education : Factor w/ 1 level "$0": 1 1 1 1 1 1 1 1 1 1 ...
$ Health.Care : Factor w/ 38 levels "-$10","-$11",..: 7 7 7 7 2 8 12 36 30 9 ...
$ Welfare : Factor w/ 1 level "$0": 1 1 1 1 1 1 1 1 1 1 ...
$ Earnings : Factor w/ 41 levels "$0","$101","$104",..: 1 1 1 22 23 24 25 26 27 28 ...
$ State.Benefits : Factor w/ 37 levels "$102","$117",..: 37 1 3 4 6 10 12 18 24 27 ...
$ Local.Benefits : Factor w/ 24 levels "$115","$136",..: 24 1 2 12 14 16 19 22 23 21 ...
$ Federal.Benefits: Factor w/ 39 levels "$0","$100","$102",..: 1 1 1 12 12 17 20 19 19 21 ...

Answer 1

If you need to only remove the $ and do not want to change the class of the columns.
indx <- sapply(data, is.factor)
data[indx] <- lapply(data[indx], function(x)
as.factor(gsub("\\$", "", x)))
If you need numeric columns, you can strip out the , as well (contributed by #David
Arenburg) and convert to numeric by as.numeric
data[indx] <- lapply(data[indx], function(x) as.numeric(gsub("[,$]", "", x)))
You can wrap this in a function
f1 <- function(dat, pat="[$]", Class="factor"){
indx <- sapply(dat, is.factor)
if(Class=="factor"){
dat[indx] <- lapply(dat[indx], function(x) as.factor(gsub(pat, "", x)))
}
else {
dat[indx] <- lapply(dat[indx], function(x) as.numeric(gsub(pat, "", x)))
}
dat
}
f1(data)
f1(data, pat="[,$]", "numeric")
data
set.seed(24)
data <- data.frame(Year=1:6, Prog.Cost= sample(c("-$3,3333", "$0"),
6, replace=TRUE), Total.Benefits= sample(c("$2,155","$2,418",
"$2,312"), 6, replace=TRUE))

Answer 2

If you have to read a lot of csv files with data like this, perhaps you should consider creating your own as method to use with the colClasses argument, like this:
setClass("dollar")
setAs("character", "dollar",
function(from)
as.numeric(gsub("[,$]", "", from, fixed = FALSE)))
Before demonstrating how to use it, let's write #akrun's sample data to a csv file named "A". This would not be necessary in your actual use case where you would be reading the file directly...
## write #akrun's sample data to a csv file named "A"
set.seed(24)
data <- data.frame(
Year=1:6,
Prog.Cost= sample(c("-$3,3333", "$0"), 6, replace = TRUE),
Total.Benefits = sample(c("$2,155","$2,418","$2,312"), 6, replace=TRUE))
A <- tempfile()
write.csv(data, A, row.names = FALSE)
Now, you have a new option for colClasses that can be used with read.csv :-)
read.csv(A, colClasses = c("numeric", "dollar", "dollar"))
# Year Prog.Cost Total.Benefits
# 1 1 -33333 2155
# 2 2 -33333 2312
# 3 3 0 2312
# 4 4 0 2155
# 5 5 0 2418
# 6 6 0 2418

Answer 3

It would probably be more beneficial to just read it again, this time with readLines. I wrote akrun's data to the file "data.text" and fixed the strings before reading the table. Nor sure if the comma was a decimal point or an annoying comma, so I chose decimal point.
r <- gsub("[$]", "", readLines("data.txt"))
read.table(text = r, dec = ",")
# Year Prog.Cost Total.Benefits
# 1 1 -3.3333 2.155
# 2 2 -3.3333 2.312
# 3 3 0.0000 2.312
# 4 4 0.0000 2.155
# 5 5 0.0000 2.418
# 6 6 0.0000 2.418