Same length for all numbers in one matrix

Question

I have a matrix which is basically like

100    2100  
31000  230  
31     9199

And I want every number to have the same size, like 100 --> 00100 or 9199 --> 09199. Do you have any suggestions for me?

Numbers have no length, character representation of numbers does... is your matrix a charater or numeric matrix ? — digEmAll, Oct 12 '13 at 12:04
He wants to format using leading zeroes, which has been asked many times before. — nograpes, Oct 12 '13 at 12:20

digEmAll · Answer 1 · 2013-10-13T09:58:33.683

2

You could use formatC:

numMx <- matrix(c(100,2100,31000,230,31,9199),nrow=3,byrow=T)

frmt <- "d"   # d --> numbers formatted as integers
minWidth <- 5 # minimum characters length of each number e.g. 42 --> "00042"

chMx <- formatC(numMx, width = minWidth, format = frmt, flag = "0")

# > chMx
#      [,1]    [,2]   
# [1,] "00100" "02100"
# [2,] "31000" "00230"
# [3,] "00031" "09199"

To automatically determine the minimum width, you can use this code:

minWidth <- max(nchar(formatC(numMx,format=frmt)))

edited Oct 13 '13 at 09:58

answered Oct 12 '13 at 12:21

digEmAll

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Added a way to automatically determine the minimum width. – digEmAll Oct 12 '13 at 12:27
+1! elegant use of `formatC`. – agstudy Oct 12 '13 at 12:58

score 2 · Accepted Answer · answered Oct 12 '13 at 12:26

2

You can use sprintf :

dat <- read.table(text='100    2100  
31000  230  
31     9199')

max.len <- max(apply(dat,2,function(x)
           nchar(as.character(x))))

matrix(sprintf(paste0("%0",max.len,"d"), unlist(dat)),
          ncol=2)

answered Oct 12 '13 at 12:26

agstudy

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+1 this was what I was thinking. Nice use to catch the max length – Simon O'Hanlon Oct 12 '13 at 12:30

alexis_laz · Answer 3 · 2013-10-12T12:32:14.647

I use the following function for same problems:

    add0 <- function(x, len) #x = number to add 0 ; len = the wanted length of the number
    {
     x.len <- length(unlist(strsplit(as.character(x), split = "")))
     ifelse(x.len < len, paste(paste(rep(0, len - x.len), collapse = ""), x, sep = ""), as.character(x))
    }

Test:

    mat <- matrix(sample(1:25, 25), 5, 5) #random matrix

    apply(mat, c(1,2), add0, len = max(nchar(as.character(mat)))) #change whole matrix using maximum "length" of its values

Same length for all numbers in one matrix

3 Answers3