Use C-style String Formatting Commands

Description

A wrapper for the C function sprintf, that returns a character vector containing a formatted combination of text and variable values.

Usage

sprintf(fmt, ...)
gettextf(fmt, ..., domain = NULL)

Arguments

Details

sprintf is a wrapper for the system sprintf C-library function. Attempts are made to check that the mode of the values passed match the format supplied, and R's special values (NA, Inf, -Inf and NaN) are handled correctly.

gettextf is a convenience function which provides C-style string formatting with possible translation of the format string.

The arguments (including fmt) are recycled if possible a whole number of times to the length of the longest, and then the formatting is done in parallel.

The following is abstracted from Kernighan and Ritchie (see References). The string fmt contains normal characters, which are passed through to the output string, and also special characters that operate on the arguments provided through .... Special characters start with a % and end with one of the letters in the set difeEgGsxX%. These letters denote the following types:

d, i, x, X

Integer value, x and X being hexadecimal (using the same case for a-f as the code). Numeric variables with exactly integer values will be coerced to integer.

f

Double precision value, in decimal notation of the form "[-]mmm.ddd". The number of decimal places is specified by the precision: the default is 6; a precision of 0 suppresses the decimal point.

e, E

Double precision value, in decimal notation of the form [-]m.ddde[+-]xx or [-]m.dddE[+-]xx.

g, G

Double precision value, in %e or %E format if the exponent is less than -4 or greater than or equal to the precision, and %f format otherwise.

s

Character string.

%

Literal % (none of the formatting characters given below are permitted in this case).

as.character is used for non-character arguments with s and as.double for non-double arguments with f, e, E, g, G. NB: the length is determined before conversion, so do not rely on the internal coercion if this would change the length.

In addition, between the initial % and the terminating conversion character there may be, in any order:

m.n

Two numbers separated by a period, denoting the field width (m) and the precision (n)

-

Left adjustment of converted argument in its field

+

Always print number with sign

a space

Prefix a space if the first number is not a sign

0

For numbers, pad to the field width with leading zeros

Further, immediately after % may come 1$ to 99$ to refer to the numbered argument: this allows arguments to be referenced out of order and is mainly intended for translators of error messages. If this is done it is best if all formats are numbered: if not the unnumbered ones process the arguments in order. See the examples.

A field width or precision (but not both) may be indicated by an asterisk *. In this case an argument specifies the desired number. A negative field width is taken as a '-' flag followed by a positive field width. A negative precision is taken as if the precision were omitted. The *1$ to *99$ notation for arguments referenced out of order is also supported.

The result has a length limit, probably 8192 bytes, and attempts to exceed this may result in an error, or truncation with a warning.

Value

A character vector of length that of the longest input. Character NAs are converted to "NA".

Author(s)

Original code by Jonathan Rougier, J.C.Rougier@durham.ac.uk.

References

Kernighan, B. W. and Ritchie, D. M. (1988) The C Programming Language. Second edition, Prentice Hall. describes the format options in table B-1 in the Appendix.

See Also

formatC for a way of formatting vectors of numbers in a similar fashion.

paste for another way of creating a vector combining text and values.

gettext for the mechanisms for the automated translation of text.

Examples

## be careful with the format: most things in R are floats
## only integer-valued reals get coerced to integer.

sprintf("%s is %f feet tall\n", "Sven", 7.1)      # OK
try(sprintf("%s is %i feet tall\n", "Sven", 7.1)) # not OK
try(sprintf("%s is %i feet tall\n", "Sven", 7))   # OK

## use a literal % :

sprintf("%.0f%% said yes (out of a sample of size %.0f)", 66.666, 3)

## various formats of pi :

sprintf("%f", pi)
sprintf("%.3f", pi)
sprintf("%1.0f", pi)
sprintf("%5.1f", pi)
sprintf("%05.1f", pi)
sprintf("%+f", pi)
sprintf("% f", pi)
sprintf("%-10f", pi) # left justified
sprintf("%e", pi)
sprintf("%E", pi)
sprintf("%g", pi)
sprintf("%g",   1e6 * pi) # -> exponential
sprintf("%.9g", 1e6 * pi) # -> "fixed"
sprintf("%G", 1e-6 * pi)

## no truncation:
sprintf("%1.f",101)

## re-use one argument three times, show difference between %x and %X
xx <- sprintf("%1$d %1$x %1$X", 0:15)
xx <- matrix(xx, dimnames=list(rep("", 16), "%d%x%X"))
noquote(format(xx, justify="right"))

## More sophisticated:

sprintf("min 10-char string '%10s'",
        c("a", "ABC", "and an even longer one"))

n <- 1:18
sprintf(paste("e with %2d digits = %.",n,"g",sep=""), n, exp(1))

## Using arguments out of order
sprintf("second %2$1.0f, first %1$5.2f, third %3$1.0f", pi, 2, 3)

## Using asterisk for width or precision
sprintf("precision %.*f, width '%*.3f'", 3, pi, 8, pi)

## Asterisk and argument re-use, 'e' example reiterated:
sprintf("e with %1$2d digits = %2$.*1$g", n, exp(1))

## re-cycle arguments 
sprintf("%s %d", "test", 1:3)