R Under development (unstable) (2023-11-16 r85542 ucrt) -- "Unsuffered Consequences"
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> library("R.utils")
Loading required package: R.oo
Loading required package: R.methodsS3
R.methodsS3 v1.8.2 (2022-06-13 22:00:14 UTC) successfully loaded. See ?R.methodsS3 for help.
R.oo v1.25.0 (2022-06-12 02:20:02 UTC) successfully loaded. See ?R.oo for help.

Attaching package: 'R.oo'

The following object is masked from 'package:R.methodsS3':

    throw

The following objects are masked from 'package:methods':

    getClasses, getMethods

The following objects are masked from 'package:base':

    attach, detach, load, save

R.utils v2.12.3 successfully loaded. See ?R.utils for help.

Attaching package: 'R.utils'

The following object is masked from 'package:utils':

    timestamp

The following objects are masked from 'package:base':

    cat, commandArgs, getOption, isOpen, nullfile, parse, warnings

> 
> # All predefined types
> print(colClasses("-?cdfilnrzDP"))
 [1] "NULL"      "NA"        "character" "double"    "factor"    "integer"  
 [7] "logical"   "numeric"   "raw"       "complex"   "Date"      "POSIXct"  
> ## [1] "NULL"      "NA"        "character" "double"
> ## [5] "factor"    "integer"   "logical"   "numeric"
> ## [9] "raw"       "complex"   "Date"      "POSIXct"
> 
> # A string in column 1, integers in column 4 and 5, rest skipped
> print(colClasses("c--ii----"))
[1] "character" "NULL"      "NULL"      "integer"   "integer"   "NULL"     
[7] "NULL"      "NULL"      "NULL"     
> ## [1] "character" "NULL"      "NULL"      "integer"
> ## [5] "integer"   "NULL"      "NULL"      "NULL"
> ## [9] "NULL"
> 
> # Repeats and custom column classes
> c1 <- colClasses("3c{MyClass}3{foo}")
> print(c1)
[1] "character" "character" "character" "MyClass"   "foo"       "foo"      
[7] "foo"      
> ## [1] "character" "character" "character" "MyClass"
> ## [5] "foo"       "foo"       "foo"
> 
> # Passing repeats and class names using sprintf() syntax
> c2 <- colClasses("%dc{%s}%d{foo}", 3, "MyClass", 3)
> stopifnot(identical(c1, c2))
> 
> # Repeats of a vector of column classes
> c3 <- colClasses("3{MyClass,c}")
> print(c3)
[1] "MyClass"   "character" "MyClass"   "character" "MyClass"   "character"
> ## [1] "MyClass"   "character" "MyClass"   "character"
> ## [4] "MyClass"   "character"
> 
> # Large number repeats
> c4 <- colClasses("321{MyClass,c,i,d}")
> c5 <- rep(c("MyClass", "character", "integer", "double"), times=321)
> stopifnot(identical(c4, c5))
> 
> proc.time()
   user  system elapsed 
   0.23    0.07    0.29