formatC {base}R Documentation

Formatting Using C-style Formats


Formatting numbers individually and flexibly, using C style format specifications. format.char is a helper function for formatC.


formatC(x, digits = NULL, width = NULL,
        format = NULL, flag = "", mode = NULL,
        big.mark = "", big.interval = 3,
      small.mark = "", small.interval = 5,
    decimal.mark = ".")

format.char(x, width = NULL, flag = "-")


x an atomic numerical or character object, typically a vector of real numbers.
digits 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.
width 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.
format 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. That 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.
flag format modifier as in Kernighan and Ritchie (1988, page 243). "0" pads leading zeros; "-" does left adjustment, others are "+", " ", and "#". There can be more than one of these, in any order.
mode "double" (or "real"), "integer" or "character". Default: Determined from the storage mode of x.
big.mark, big.interval, small.mark, small.interval, decimal.mark used for prettying longer decimal sequences, passed to prettyNum: that help page explains the details.


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.


A character object of same size and attributes as x. Unlike format, each number is formatted individually. Looping over each element of x, sprintf(...) is called (inside the C function str_signif).
format.char(x) and formatC, for character x, do simple (left or right) padding with white space.


Originally written by Bill Dunlap, later much improved by Martin Maechler, it was first adapted for R by Friedrich Leisch.


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

See Also

format, sprintf for more general C like formatting.


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

format.char(c("a", "Abc", "no way"), wid = -7)  # <=> flag = "-"
formatC(    c("a", "Abc", "no way"), wid = -7)  # <=> flag = "-"
formatC(c((-1:1)/0,c(1,100)*pi), wid=8, dig=1)

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, format="f", dig=80)#>> also long strings

[Package base version 2.1.0 Index]