Dynamically numbering files in R with placeholders using an If-elseif - r

Question

I have a vector
x <- c(1,90,233)
I need to convert this to a vector of the form:
result = c("001.csv","090.csv","233.csv")
This is the function that I wrote to perform this operation:
convert <- function(x){
for (a in 1:length(x)){
if (x[a]<10) {
x[a]<- paste("00",x[a],".csv",sep="")
}
else if (x[a] < 100) {
x[a]<- paste("0", x[a], ".csv",sep="")
}
else {
x[a]<-paste(x[a],".csv",sep="")
}
}
x
}
The output I got was:
[1] "001.csv","90.csv","233.csv"
So, a[2] is 90 was processed in the else part and not the else if part. Then I changed the else if condition to x[a]<=99
convert <- function(x){
for (a in 1:length(x)){
if (x[a]<10) {
x[a]<- paste("00",x[a],".csv",sep="")
}
else if (x[a] <= 99) {
x[a]<- paste("0", x[a], ".csv",sep="")
}
else {
x[a]<-paste(x[a],".csv",sep="")
}
}
x
}
I got this output:
[1] "001.csv" "090.csv" "0233.csv"
Now both x[2] and x[3] ie 90 and 233 are being processed in the ElseIf part. What am I doing wrong here? And how do I get the output I need?

Answer 1

This is a little bit more dynamic as you do not need to specify the number of places held by the largest number.
Step 1:
Obtain the maximum number of places held.
(nb = max(nchar(x)))
To get:
3
Step 2:
Paste the number into a sprintf() call that will automatically format the digit.
sprintf("%0*d.csv", nb, x)
To get:
[1] "001.csv" "090.csv" "233.csv"

Answer 2

The problem is that the first round of your loop makes a character, that converts the whole vector to type character. You can get around that using nchar
convert <- function(x){
for (a in 1:length(x)){
if (nchar(x[a]) == 1) {
x[a]<- paste("00",x[a],".csv",sep="")
}
else if (nchar(x[a]) == 2) {
x[a]<- paste("0", x[a], ".csv",sep="")
}
else {
x[a]<-paste(x[a],".csv",sep="")
}
}
x
}

Answer 3

sprintf("%03d", x)
[1] "001" "090" "233"
You can avoid a call to paste by including the ".csv" in the format string:
sprintf("%03d.csv", x)
[1] "001.csv" "090.csv" "233.csv"
The problem with the original code is the conversion to character, which happens on the first element.
Here's the conversion to character:
> x <- c(1, 90, 233)
> x
[1] 1 90 233
> x[1] <- "001.csv"
> x
[1] "001.csv" "90" "233"
Here's the resulting comparison of the second element:
> "90" <= 99
[1] TRUE
> "90" < 100
[1] FALSE
Similarly for the third:
> "233" < 100
[1] FALSE
> "233" <= 99
[1] TRUE
In all of these cases, the right-hand side is converted to character, then the comparison is made, as character strings.

Answer 4

Your code doesn't work as expected because the whole vector gets converted into a character vector after first assignment(conversion of numeric to character).
Please note that when a string is compared to digit, the characters are matched one by one. For eg. if you compare "90" to 100 then 9 is compared to 1, hence control goes to the else part and in the case of comparison of "233" to 99, 2 is compared 9.
You can get around this by assigning the changed values to another vector.Or, you could use the str_pad function from the stringr package.
library(stringr)
x=c(1,90,233)
padded_name= str_pad(x,width=3,side="left",pad="0")
file_name = paste0(padded_name, ".csv")