[r] How to add leading zeros?

I have a set of data which looks something like this:

anim <- c(25499,25500,25501,25502,25503,25504)
sex  <- c(1,2,2,1,2,1)
wt   <- c(0.8,1.2,1.0,2.0,1.8,1.4)
data <- data.frame(anim,sex,wt)

data
   anim sex  wt anim2
1 25499   1 0.8     2
2 25500   2 1.2     2
3 25501   2 1.0     2
4 25502   1 2.0     2
5 25503   2 1.8     2
6 25504   1 1.4     2

I would like a zero to be added before each animal id:

data
   anim sex  wt anim2
1 025499   1 0.8     2
2 025500   2 1.2     2
3 025501   2 1.0     2
4 025502   1 2.0     2
5 025503   2 1.8     2
6 025504   1 1.4     2

And for interest sake, what if I need to add two or three zeros before the animal id's?

For a general solution that works regardless of how many digits are in data$anim, use the sprintf function. It works like this:

sprintf("%04d", 1)
# [1] "0001"
sprintf("%04d", 104)
# [1] "0104"
sprintf("%010d", 104)
# [1] "0000000104"

In your case, you probably want: data$anim <- sprintf("%06d", data$anim)

str_pad from the stringr package is an alternative.

anim = 25499:25504
str_pad(anim, width=6, pad="0")

Here is another alternative for adding leading to 0s to strings such as CUSIPs which can sometimes look like a number and which many applications such as Excel will corrupt and remove the leading 0s or convert them to scientific notation.

When I tried the answer provided by @metasequoia the vector returned had leading spaces and not 0s. This was the same problem mentioned by @user1816679 -- and removing the quotes around the 0 or changing from %d to %s did not make a difference either. FYI, I am using RStudio Server running on an Ubuntu Server. This little two-step solution worked for me:

gsub(pattern = " ", replacement = "0", x = sprintf(fmt = "%09s", ids[,CUSIP]))

using the %>% pipe function from the magrittr package it could look like this:

sprintf(fmt = "%09s", ids[,CUSIP]) %>% gsub(pattern = " ", replacement = "0", x = .)

I'd prefer a one-function solution, but it works.

Here's a generalizable base R function:

pad_left <- function(x, len = 1 + max(nchar(x)), char = '0'){

    unlist(lapply(x, function(x) {
        paste0(
            paste(rep(char, len - nchar(x)), collapse = ''),
            x
        )
    }))
}

pad_left(1:100)

I like sprintf but it comes with caveats like:

however the actual implementation will follow the C99 standard and fine details (especially the behaviour under user error) may depend on the platform

For other circumstances in which you want the number string to be consistent, I made a function.

Someone may find this useful:

idnamer<-function(x,y){#Alphabetical designation and number of integers required
    id<-c(1:y)
    for (i in 1:length(id)){
         if(nchar(id[i])<2){
            id[i]<-paste("0",id[i],sep="")
         }
    }
    id<-paste(x,id,sep="")
    return(id)
}
idnamer("EF",28)

Sorry about the formatting.

data$anim <- sapply(0, paste0,data$anim)

Expanding on @goodside's repsonse:

In some cases you may want to pad a string with zeros (e.g. fips codes or other numeric-like factors). In OSX/Linux:

> sprintf("%05s", "104")
[1] "00104"

But because sprintf() calls the OS's C sprintf() command, discussed here, in Windows 7 you get a different result:

> sprintf("%05s", "104")
[1] "  104"

So on Windows machines the work around is:

> sprintf("%05d", as.numeric("104"))
[1] "00104"