Use C-style String Formatting Commands
A wrapper for the C function
sprintf, that returns a character
vector containing a formatted combination of text and variable values.
sprintf(fmt, ...) gettextf(fmt, ..., domain = NULL)
- a character vector of format strings, each of up to 8192 bytes.
- values to be passed into
fmt. Only logical, integer, real and character vectors are supported, but some coercion will be done: see the Details section.
sprintf is a wrapper for the system
function. Attempts are made to check that the mode of the values
passed match the format supplied, and R's special values (
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. Zero-length arguments are allowed and will give
a zero-length result. All arguments are evaluated even if unused, and
hence some types (e.g.,
typeof) are not allowed.
The following is abstracted from Kernighan and Ritchie (see References): however the actual implementation will follow the C99 standard and fine details (especially the behaviour under user error) may depend on the platform.
fmt contains normal characters,
which are passed through to the output string, and also conversion
specifications which operate on the arguments provided through
.... The allowed conversion specifications start with a
% and end with one of the letters in the set
aAdifeEgGosxX%. These letters denote the following types:
Xbeing hexadecimal (using the same case for
a-fas the code). Numeric variables with exactly integer values will be coerced to integer. Formats
ican also be used for logical variables, which will be converted to
NaNor (perhaps a sign followed by)
%Eformat if the exponent is less than -4 or greater than or equal to the precision, and
%fformat otherwise. (The precision (default 6) specifies the number of significant digits here, whereas in
%f, %e, it is the number of digits after the decimal point.)
[-]0xh.hhhp[+-]d. This is a binary fraction expressed in hex multiplied by a (decimal) power of 2. The number of hex digits after the decimal point is specified by the precision: the default is enough digits to represent exactly the internal binary representation. Non-finite values are converted to
NaNor (perhaps a sign followed by)
%auses lower-case for
pand the hex values: format
This should be supported on all platforms as it is a feature of C99.
The format is not uniquely defined: although it would be possible
to make the leading
h always zero or one, this is not
always done. Most systems will suppress trailing zeros, but a few
do not. On a well-written platform, for normal numbers there will
be a leading one before the decimal point plus (by default) 13
hexadecimal digits, hence 53 bits. The treatment of denormalized
(aka subnormal) numbers is very platform-dependent.
NAs are converted to
%(none of the extra formatting characters given below are permitted in this case).
as.character is used for non-character
s and by
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. The coercion is done only
once, so if
length(fmt) > 1 then all elements must expect the
same types of arguments.
In addition, between the initial
% and the terminating
conversion character there may be, in any order:
- Two numbers separated by a period, denoting the
field width (
m) and the precision (
0Xwill be prefixed to a non-zero result. For
G, the output will always have a decimal point; for
G, trailing zeros will not be removed.
Further, immediately after
% may come
to refer to 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. This notation allows arguments to be used more than
once, in which case they must be used as the same type (integer,
double or character).
A field width or precision (but not both) may be indicated by an
*: 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 treated as if the
precision were omitted. The argument should be integer, but a double
argument will be coerced to integer.
There is a limit of 8192 bytes on elements of
fmt, and on
strings included from a single
Field widths and precisions of
%s conversions are interpreted
as bytes, not characters, as described in the C standard.
The C doubles used for R numerical vectors have signed zeros, which
sprintf may output as
A character vector of length that of the longest input. If any
fmtor any character argument is declared as UTF-8, the element of the result will be in UTF-8 and have the encoding declared as UTF-8. Otherwise it will be in the current locale's encoding.
The format string is passed down the OS's
sprintf function, and
incorrect formats can cause the latter to crash the R process . R
does perform sanity checks on the format, but not all possible user
errors on all platforms have been tested, and some might be terminal. The behaviour on inputs not documented here is undefined,
which means it is allowed to differ by platform.
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.
The C Standards, especially ISO/IEC 9899:1999 for C99. Links can be found at http://developer.r-project.org/Portability.html.
man sprintf on a Unix-alike system.
formatC for a way of formatting vectors of numbers in a
paste for another way of creating a vector combining
text and values.
gettext for the mechanisms for the automated translation
## 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 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")) ## Platform-dependent bad example from qdapTools 1.0.0: ## may pad with spaces or zeroes. sprintf("%09s", month.name) n <- 1:18 sprintf(paste0("e with %2d digits = %.", n, "g"), 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) ## binary output showing rounding/representation errors x <- seq(0, 1.0, 0.1); y <- c(0,.1,.2,.3,.4,.5,.6,.7,.8,.9,1) cbind(x, sprintf("%a", x), sprintf("%a", y))