Use C-style String Formatting Commands

Description

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

Usage

sprintf(fmt, ...)

Arguments

Details

This 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.

The following is abstracted from K&R (see References, below). 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 terminate with one of the letters in the set difeEgGs%. These letters denote the following types:

d,i

Integer value

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)

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

Value

A character vector of length one. 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.

Examples

## be careful with the format: most things in R are floats

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

## 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)

## More sophisticated:

lapply(c("a", "ABC", "and an even longer one"),
       function(ch) sprintf("10-string '%10s'", ch))

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