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A binary operator on strings with units in them

grapes-as-grapes.Rd

The function calls the units utility and converts the string on the left into the unit on the right, e.g.: "cm" %as% "inches", both units can contain numbers. Any input that is accepted by the units utility is acceptable, as long as it makes sense with the command line arguments: units -t "$originalUnit" "$targetUnit"

Usage

txtUnit %as% target

Arguments

txtUnit

a string with numeric values, including units, e.g. "3 cm"

target

string, target unit, e.g. "m", must be scalar

Value

a numeric value y: valoriginalUnit = ytargetUnit, the target unit is attached to the returned value, as a comment.

Details

FreeBSD and MacOS have a buggy units command: it fails to signal failure, so this function does some additional checks to make sure that the conversion worked.

Examples

  ## needs `units` utility (a system utility)
  if (nzchar(Sys.which("units"))){
      y <- "21 cm" %as% "inches"
      print(y)
      y <- "12 nmol/L" %as% "mol/L"
      print(y)
      y <- "12 mol/m^3" %as% "mmol/L"
      print(y)
  }
#>       21 cm 
#> "8.2677165" 
#> attr(,"unit")
#> [1] "inches"
#> 12 nmol/L 
#> "1.2e-08" 
#> attr(,"unit")
#> [1] "mol/L"
#> 12 mol/m^3 
#>       "12" 
#> attr(,"unit")
#> [1] "mmol/L"