formatC {base}R Documentation

Formatting Using C-style Formats


Formatting numbers individually and flexibly, formatC() using C style format specifications.

prettyNum() is used for “prettifying” (possibly formatted) numbers, also in format.default.

.format.zeros(), an auxiliary function of prettyNum() re-formats the zeros in a vector x of formatted numbers.


formatC(x, digits = NULL, width = NULL,
        format = NULL, flag = "", mode = NULL,
        big.mark = "", big.interval = 3L,
        small.mark = "", small.interval = 5L,
        decimal.mark = getOption("OutDec"),
        preserve.width = "individual", zero.print = NULL,
        drop0trailing = FALSE)

prettyNum(x, big.mark = "",   big.interval = 3L,
          small.mark  = "", small.interval = 5L,
          decimal.mark = getOption("OutDec"), input.d.mark = decimal.mark,
          preserve.width = c("common", "individual", "none"),
          zero.print = NULL, drop0trailing = FALSE, is.cmplx = NA,

.format.zeros(x, zero.print, nx = suppressWarnings(as.numeric(x)))



an atomic numerical or character object, possibly complex only for prettyNum(), typically a vector of real numbers. Any class is discarded, with a warning.


the desired number of digits after the decimal point (format = "f") or significant digits (format = "g", = "e" or = "fg").

Default: 2 for integer, 4 for real numbers. If less than 0, the C default of 6 digits is used. If specified as more than 50, 50 will be used with a warning unless format = "f" where it is limited to typically 324. (Not more than 15–21 digits need be accurate, depending on the OS and compiler used. This limit is just a precaution against segfaults in the underlying C runtime.)


the total field width; if both digits and width are unspecified, width defaults to 1, otherwise to digits + 1. width = 0 will use width = digits, width < 0 means left justify the number in this field (equivalent to flag = "-"). If necessary, the result will have more characters than width. For character data this is interpreted in characters (not bytes nor display width).


equal to "d" (for integers), "f", "e", "E", "g", "G", "fg" (for reals), or "s" (for strings). Default is "d" for integers, "g" for reals.

"f" gives numbers in the usual format; "e" and "E" give n.ddde+nn or n.dddE+nn (scientific format); "g" and "G" put x[i] into scientific format only if it saves space to do so.

"fg" uses fixed format as "f", but digits as the minimum number of significant digits. This can lead to quite long result strings, see examples below. Note that unlike signif this prints large numbers with more significant digits than digits. Trailing zeros are dropped in this format, unless flag contains "#".


for formatC, a character string giving a format modifier as in Kernighan and Ritchie (1988, page 243) or the C+99 standard. "0" pads leading zeros; "-" does left adjustment, others are "+", " ", and "#"; on some platform–locale combination, "'" activates “thousands' grouping” for decimal conversion, and versions of ‘glibc’ allow "I" for integer conversion to use the locale's alternative output digits, if any.

There can be more than one of these, in any order. Other characters used to have no effect for character formatting, but signal an error since R 3.4.0.


"double" (or "real"), "integer" or "character". Default: Determined from the storage mode of x.


character; if not empty used as mark between every big.interval decimals before (hence big) the decimal point.


see big.mark above; defaults to 3.


character; if not empty used as mark between every small.interval decimals after (hence small) the decimal point.


see small.mark above; defaults to 5.


the character to be used to indicate the numeric decimal point.


if x is character, the character known to have been used as the numeric decimal point in x.


string specifying if the string widths should be preserved where possible in those cases where marks (big.mark or small.mark) are added. "common", the default, corresponds to format-like behavior whereas "individual" is the default in formatC(). Value can be abbreviated.


logical, character string or NULL specifying if and how zeros should be formatted specially. Useful for pretty printing ‘sparse’ objects.


logical, indicating if trailing zeros, i.e., "0" after the decimal mark, should be removed; also drops "e+00" in exponential formats.


optional logical, to be used when x is "character" to indicate if it stems from complex vector or not. By default (NA), x is checked to ‘look like’ complex.


arguments passed to format.


numeric vector of the same length as x, typically the numbers of which the character vector x is the pre-format.


If you set format it overrides the setting of mode, so formatC(123.45, mode = "double", format = "d") gives 123.

The rendering of scientific format is platform-dependent: some systems use n.ddde+nnn or n.dddenn rather than n.ddde+nn.

formatC does not necessarily align the numbers on the decimal point, so formatC(c(6.11, 13.1), digits = 2, format = "fg") gives c("6.1", " 13"). If you want common formatting for several numbers, use format.

prettyNum is the utility function for prettifying x. x can be complex (or format(<complex>), here. If x is not a character, format(x[i], ...) is applied to each element, and then it is left unchanged if all the other arguments are at their defaults. Use the input.d.mark argument for prettyNum(x) when x is a character vector not resulting from something like format(<number>) with a period as decimal mark.

Because gsub is used to insert the big.mark and small.mark, special characters need escaping. In particular, to insert a single backslash, use "\\\\".

The C doubles used for R numerical vectors have signed zeros, which formatC may output as -0, -0.000 ....

There is a warning if big.mark and decimal.mark are the same: that would be confusing to those reading the output.


A character object of same size and attributes as x (after discarding any class), in the current locale's encoding.

Unlike format, each number is formatted individually. Looping over each element of x, the C function sprintf(...) is called for numeric inputs (inside the C function str_signif).

formatC: for character x, do simple (left or right) padding with white space.


Prior to R 3.0.2 this copied the class of x to the return value and could easily create invalid objects.

The default for decimal.mark in formatC() was changed in R 3.2.0: for use within print methods in packages which might be used with earlier versions: use decimal.mark = getOption("OutDec") explicitly.


formatC was originally written by Bill Dunlap for S-PLUS, later much improved by Martin Maechler.

It was first adapted for R by Friedrich Leisch and since much improved by the R Core team.


Kernighan, B. W. and Ritchie, D. M. (1988) The C Programming Language. Second edition. Prentice Hall.

See Also


sprintf for more general C-like formatting.


xx  <- pi * 10^(-5:4)
cbind(format(xx, digits = 4), formatC(xx))
cbind(formatC(xx, width = 9, flag = "-"))
cbind(formatC(xx, digits = 5, width = 8, format = "f", flag = "0"))
cbind(format(xx, digits = 4), formatC(xx, digits = 4, format = "fg"))

formatC(    c("a", "Abc", "no way"), width = -7)  # <=> flag = "-"
formatC(c((-1:1)/0,c(1,100)*pi), width = 8, digits = 1)

## note that some of the results here depend on the implementation
## of long-double arithmetic, which is platform-specific.
xx <- c(1e-12,-3.98765e-10,1.45645e-69,1e-70,pi*1e37,3.44e4)
##       1        2             3        4      5       6
formatC(xx, format = "fg")       # special "fixed" format.
formatC(xx[1:4], format = "f", digits = 75) #>> even longer strings

formatC(c(3.24, 2.3e-6), format = "f", digits = 11, drop0trailing = TRUE)

r <- c("76491283764.97430", "29.12345678901", "-7.1234", "-100.1","1123")
## American:
prettyNum(r, big.mark = ",")
## Some Europeans:
prettyNum(r, big.mark = "'", decimal.mark = ",")

(dd <- sapply(1:10, function(i) paste((9:0)[1:i], collapse = "")))
prettyNum(dd, big.mark = "'")

## examples of 'small.mark'
pN <- stats::pnorm(1:7, lower.tail = FALSE)
cbind(format (pN, small.mark = " ", digits = 15))
cbind(formatC(pN, small.mark = " ", digits = 17, format = "f"))

cbind(ff <- format(1.2345 + 10^(0:5), width = 11, big.mark = "'"))
## all with same width (one more than the specified minimum)

## individual formatting to common width:
fc <- formatC(1.234 + 10^(0:8), format = "fg", width = 11, big.mark = "'")
## Powers of two, stored exactly, formatted individually:
pow.2 <- formatC(2^-(1:32), digits = 24, width = 1, format = "fg")
## nicely printed (the last line showing 5^32 exactly):

## complex numbers:
r <- 10.0000001; rv <- (r/10)^(1:10)
(zv <- (rv + 1i*rv))
op <- options(digits = 7) ## (system default)
(pnv <- prettyNum(zv))
stopifnot(pnv == "1+1i", pnv == format(zv),
          pnv == prettyNum(zv, drop0trailing = TRUE))
## more digits change the picture:
options(digits = 8)
head(fv <- format(zv), 3)
prettyNum(fv, drop0trailing = TRUE) # a bit nicer

## The  '  flag :
doLC <- FALSE # R warns, so change to TRUE manually if you want see the effect
  oldLC <- Sys.setlocale("LC_NUMERIC", "de_CH.UTF-8")
formatC(1.234 + 10^(0:4), format = "fg", width = 11, flag = "'")
## -->  .....  "      1'001" "     10'001"   on supported platforms
if(doLC) ## revert, typically to  "C"  :
  Sys.setlocale("LC_NUMERIC", oldLC)

[Package base version 3.4.0 Index]