R Sort strings according to substring

Question

I have a set of file names like:

filelist <- c("filea-10.txt", "fileb-2.txt", "filec-1.txt", "filed-5.txt", "filef-4.txt")

and I would like to filter them according to the number after "-".

In python, for instance, I can use the keyparameter of the sorting function:

filelist <- ["filea-10.txt", "fileb-2.txt", "filec-1.txt", "filed-5.txt", "filef-4.txt"]
sorted(filelist, key=lambda(x): int(x.split("-")[1].split(".")[0]))

> ["filec-1.txt", "fileb-2.txt", "filef-4.txt", "filed-5.txt", "filea-10.txt"]

In R, I am playing with strsplit and lapply with no luck so far.

Which is the way to do it in R?

Edit: File names can be many things and may include more numbers. The only fixed pattern is that the number I want to sort by is after the "-". Another (real) example:

c <- ("boards10017-51.mp4",  "boards10065-66.mp4",  "boards10071-81.mp4",
      "boards10185-91.mp4", "boards10212-63.mp4",  "boards1025-51.mp4",   
      "boards1026-71.mp4",   "boards10309-89.mp4", "boards10310-68.mp4",  
      "boards10384-50.mp4",  "boards10398-77.mp4",  "boards10419-119.mp4", 
      "boards10421-85.mp4",  "boards10444-87.mp4",  "boards10451-60.mp4",  
      "boards10461-81.mp4",  "boards10463-52.mp4",  "boards10538-83.mp4",  
      "boards10575-62.mp4",  "boards10577-249.mp4")"

Will there always just be one number? Can't you just extract the numbers and order by that? — A5C1D2H2I1M1N2O1R2T1
– A5C1D2H2I1M1N2O1R2T1, Commented May 30, 2015 at 5:46
No, sorry. There are more numbers. A real example is boards451-74. I'll edit. — alberto
– alberto, Commented May 30, 2015 at 5:57

A5C1D2H2I1M1N2O1R2T1 · Accepted Answer · 2015-05-30 06:04:44Z

10

I'm not sure of the actual complexity of your list of file names, but something like the following might be sufficient:

filelist[order(as.numeric(gsub("[^0-9]+", "", filelist)))]
# [1] "filec-1.txt"  "fileb-2.txt"  "filef-4.txt"  "filed-5.txt"  "filea-10.txt"

Considering your edit, you may want to change the gsub to something like:

gsub(".*-|\\..*", "", filelist)

Again, without a few more text cases, it's hard to say whether this is sufficient for your needs.

Example:

 x <- c("boards10017-51.mp4", "boards10065-66.mp4", "boards10071-81.mp4", 
     "boards10185-91.mp4", "boards10212-63.mp4", "boards1025-51.mp4",     
     "boards1026-71.mp4", "boards10309-89.mp4", "boards10310-68.mp4",     
     "boards10384-50.mp4", "boards10398-77.mp4", "boards10419-119.mp4",   
     "boards10421-85.mp4", "boards10444-87.mp4", "boards10451-60.mp4",    
     "boards10461-81.mp4", "boards10463-52.mp4", "boards10538-83.mp4",    
     "boards10575-62.mp4", "boards10577-249.mp4")  

x[order(as.numeric(gsub(".*-|\\..*", "", x)))]
##  [1] "boards10384-50.mp4"  "boards10017-51.mp4"  "boards1025-51.mp4"  
##  [4] "boards10463-52.mp4"  "boards10451-60.mp4"  "boards10575-62.mp4" 
##  [7] "boards10212-63.mp4"  "boards10065-66.mp4"  "boards10310-68.mp4" 
## [10] "boards1026-71.mp4"   "boards10398-77.mp4"  "boards10071-81.mp4" 
## [13] "boards10461-81.mp4"  "boards10538-83.mp4"  "boards10421-85.mp4" 
## [16] "boards10444-87.mp4"  "boards10309-89.mp4"  "boards10185-91.mp4" 
## [19] "boards10419-119.mp4" "boards10577-249.mp4"

edited May 30, 2015 at 6:04

answered May 30, 2015 at 5:48

A5C1D2H2I1M1N2O1R2T1

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1 Comment

Jota Over a year ago

Could also target the numbers directly: sub(".*-(\\d+).*", "\\1", x)

Andre Elrico · Accepted Answer · 2018-06-15 10:09:29Z

I made a regEx sort function:

function:

reg_sort <- function(x,...,verbose=F) {
    ellipsis <-   sapply(as.list(substitute(list(...)))[-1], deparse, simplify="array")
    reg_list <-   paste0(ellipsis, collapse=',')
    reg_list %<>% strsplit(",") %>% unlist %>% gsub("\\\\","\\",.,fixed=T)
    pattern  <-   reg_list %>% map_chr(~sub("^-\\\"","",.) %>% sub("\\\"$","",.) %>% sub("^\\\"","",.) %>% trimws)
    descInd  <-   reg_list %>% map_lgl(~grepl("^-\\\"",.)%>%as.logical)

    reg_extr <-   pattern %>% map(~str_extract(x,.)) %>% c(.,list(x)) %>% as.data.table
    reg_extr[] %<>% lapply(., function(x) type.convert(as.character(x), as.is = TRUE))

    map(rev(seq_along(pattern)),~{reg_extr<<-reg_extr[order(reg_extr[[.]],decreasing = descInd[.])]})

    if(verbose) { tmp<-lapply(reg_extr[,.SD,.SDcols=seq_along(pattern)],unique);names(tmp)<-pattern;tmp %>% print }

    return(reg_extr[[ncol(reg_extr)]])
}

data:

filelist <- c("filea-10.txt", "fileb-2.txt", "filec-1.txt", "filed-5.txt", "filef-4.txt")

call function

reg_sort(filelist,"\\d+")
#[1] "filec-1.txt"  "fileb-2.txt"  "filef-4.txt"  "filed-5.txt"  "filea-10.txt"

other features are:

Sort descending: reg_sort(filelist,-"\\d+")

#[1] "filea-10.txt" "filed-5.txt" "filef-4.txt" "fileb-2.txt" "filec-1.txt"
Multi layer sorting: reg_sort(filelist,-"\\d+","\\w") (does not make sense with this example data)
Verbose mode: reg_sort(filelist,"\\d+",verbose=T) (see/check what the regEx pattern has extracted in order to sort)

$\\d+ [1] 1 2 4 5 10

[1] "filec-1.txt" "fileb-2.txt" "filef-4.txt" "filed-5.txt" "filea-10.txt"

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