formatC

0th

Percentile

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.

Keywords
print, character
Usage
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)))
Arguments
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.
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. 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.)

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. For character data this is interpreted in characters (not bytes nor display 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 xxx.xxx 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 "#".

flag
For formatC, a character string giving a 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
character; if not empty used as mark between every big.interval decimals before (hence big) the decimal point.
big.interval
see big.mark above; defaults to 3.
small.mark
character; if not empty used as mark between every small.interval decimals after (hence small) the decimal point.
small.interval
see small.mark above; defaults to 5.
decimal.mark
the character to be used to indicate the numeric decimal point.
input.d.mark
if x is character, the character known to have been used as the numeric decimal point in x.
preserve.width
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.
zero.print
logical, character string or NULL specifying if and how zeros should be formatted specially. Useful for pretty printing ‘sparse’ objects.
drop0trailing
logical, indicating if trailing zeros, i.e., "0" after the decimal mark, should be removed; also drops "e+00" in exponential formats.
is.cmplx
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.
nx
numeric vector of the same length as x, typically the numbers of which the character vector x is the pre-format.
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.

prettyNum is the utility function for prettifying x. x can be complex (or format(), 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() 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.

Value

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.

Note

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.

References

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.

Aliases
  • formatC
  • prettyNum
  • .format.zeros
Examples
library(base) 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) 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 = "'") cbind(fc) ## 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): noquote(cbind(pow.2)) ## 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) prettyNum(fv, drop0trailing = TRUE) # a bit nicer options(op)
Documentation reproduced from package base, version 3.3, License: Part of R @VERSION@

Community examples

richie@datacamp.com at Jan 22, 2017 base v3.3.2

# `formatC()` `formatC()` is based upon the C/C++ function `printf()`. The [documentation](http://www.cplusplus.com/reference/cstdio/printf) for that function contains details on how many of the arguments to `formatC()` work. ## Basic usage `formatC()` takes a numeric vector as an input and returns a character vector. With no arguments other than `x`, `formatC()` works like [`signif()`](https://www.rdocumentation.org/packages/base/topics/signif) + [`as.character()`](https://www.rdocumentation.org/packages/base/topics/character), (though with different rules for rounding). ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x) as.character(signif(x, 4)) ``` ## `digits` and `format` arguments These arguments affect each other, and need to be discussed together. `format` determines whether the numbers should be displayed using fixed, scientific, or integer-like formatting. `digits` determines either the number of _significant digits_ or the number of _decimal paces_ to round the numbers to, depending upon the value of `format`. Note that the documentation is apparently wrong (as of v3.3.2) – the default value of `digits` is always 4, even for `integer` inputs. `format = "d"` treats the numbers as integers, so nothing after the decimal place is shown. Conversion to integer using [`as.integer()`](https://www.rdocumentation.org/packages/base/topics/integer) is shown for comparison. ```{r} (x <- c(1.2345, 6.789) * 10 ^ (-2:3) * c(1, -1, 1)) formatC(x, format = "d") as.character(as.integer(x)) ``` `format = "e"` uses scientific formatting. In this case, `digits` refers to the number of significant digits to round each number to. See [`signif()`](https://www.rdocumentation.org/packages/base/topics/signif) for comparison. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "e", digits = 1) formatC(x, format = "e", digits = 2) formatC(x, format = "e", digits = 3) formatC(x, format = "e") # implicitly digits = 4 formatC(x, format = "e", digits = 5) ``` `format = "E"` is a variant of `format = "e"` that prints an upper-case `"E"` to denote the start of the exponent. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "E") ``` `format = "f"` uses fixed formatting. In this case, `digits` refers to the number of decimal places to round each number to. See [`round()`](https://www.rdocumentation.org/packages/base/topics/round) for comparison. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "f", digits = 1) formatC(x, format = "f", digits = 2) formatC(x, format = "f", digits = 3) formatC(x, format = "f") # implicitly digits = 4 formatC(x, format = "f", digits = 5) ``` `format = "g"` automatically mixes fixed or scientific, trying to choose whichever takes the least amount of space. `digits` refers to significant digits. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "g", digits = 1) formatC(x, format = "g", digits = 2) formatC(x, format = "g", digits = 3) formatC(x, format = "g") # implicitly digits = 4 formatC(x, format = "g", digits = 5) ``` `format = "G"` is a variant of `format = "g"` that prints an upper-case `"E"` to denote the start of the exponent in scientifically formatted values. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "G") ``` `format = "fg"` works like `format = "g"`, except that `digits` refers to decimal places. In this case, trailing zeroes are dropped. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "fg", digits = 1) formatC(x, format = "fg", digits = 2) formatC(x, format = "fg", digits = 3) formatC(x, format = "fg") # implicitly digits = 4 formatC(x, format = "fg", digits = 5) ``` Negative values of `digits` are treated as `digits = 6`. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "e", digits = -1) formatC(x, format = "f", digits = -1) ``` The largest allowed value of `digits` is `324` when `format = "f"`, and 50 otherwise. Note that under most circumstances, you won't be better than 15 significant figures of accuracy, so the rest will be gibberish. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "f", digits = 325) formatC(x, format = "e", digits = 51) ``` `format = "s"` is a little different. It is designed to be used with an input that is already contains strings (rather than numbers). It's main purpose is to be used with the `width` argument (see below) to pad strings to a specified number of characters. ## `width` argument `width` specifies the minimum number of characters of each element of the result. If the number is too short, it is padded on the left with spaces. This is mostly useful for getting columns of numbers to line up. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "f", width = 6) formatC(x, format = "f", width = 7) formatC(x, format = "f", width = 8) formatC(x, format = "f", width = 9) ``` You can specify a negative width to pad on the right instead. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "f", width = -6) formatC(x, format = "f", width = -7) formatC(x, format = "f", width = -8) formatC(x, format = "f", width = -9) ``` `width = 0` is interpreted as `width = digits`, in which case you should never have padding. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, format = "f", digits = 8, width = 0) formatC(x, format = "f", digits = 8, width = 8) ``` ## `flag` argument There are five modifying flags available: `+`, `` ``, `-`, `0`, and `#`. `flag` takes a sting containing zero or more of these flags in any order. `flag = "+"` means that positive numbers are prefixed with a plus sign. ```{r} (x <- c(1, -1, 1) * 1.2345 * 10 ^ (-4:4)) formatC(x, flag = "+") ``` `flag = "+"` means that positive numbers are prefixed with a space. When `flag = "+ "`, the plus sign takes priority. ```{r} (x <- c(1, -1, 1) * 1.2345 * 10 ^ (-4:4)) formatC(x, flag = " ") # space flag ignored formatC(x, flag = "+ ") formatC(x, flag = " +") ``` `flag = "-"` means pad short strings on the right, exactly like using a negative `width`. Using `flag = "-"` and a negative `width` _doesn't_ double reverse the padding; it still pads on the right. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, width = 10, flag = "-") formatC(x, width = -10, flag = "-") ``` `flag = "0"` means pad short strings with zeroes, not spaces. It cannot be used in combination with `flag = "-"` to pad with zeroes on the right. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, width = 10, flag = "0") formatC(x, width = 10, flag = "-0") # zero flag ignored ``` `flag = "#"` prints a trailing decimal point in the case where `digits = 0`. ```{r} (x <- 1.2345 * 10 ^ (-4:4)) formatC(x, digits = 0, format = "e") formatC(x, digits = 0, format = "e", flag = "#") formatC(x, digits = 0, format = "f") formatC(x, digits = 0, format = "f", flag = "#") formatC(x, digits = 0, format = "g") formatC(x, digits = 0, format = "g", flag = "#") ``` ## `big.mark` and `big.interval` arguments When the format is a fixed type (`format %in% c("d", "f", "fg")`), `big.mark` and `big.interval` control separators of digits before the decimal point. For example, in the USA, monetary quantities are often separated the a comma after every 3 digits. In France, monetary quantities are separated by a space every three digits. See [`Sys.localeconv()`](https://www.rdocumentation.org/packages/base/topics/Sys.localeconv) and the C++ documentation for [`lconv` structures](http://www.cplusplus.com/reference/clocale/lconv) describe the correct formatting for numbers in a given locale. In particular, note the `thousands_sep`, `grouping`, `mon_thousands_sep`, and `mon_grouping` elements. ```{r} (x <- 1.2345 * 10 ^ (1:10)) formatC(x, format = "d", big.mark = ",", big.interval = 3) formatC(x, format = "d", big.mark = " ", big.interval = 3) ``` ## `small.mark`, `small.interval`, and `decimal.mark` arguments These work in in a similar way to `big.mark` and `big.interval`, but they control the decimal place, and what happens afterwards. Use of these arguments only makes sense when `format %in% c("f", "fg")`. ```{r} (x <- 1.2345 * 10 ^ (0:-10)) formatC(x, format = "fg", decimal.mark = ".", small.mark = ",", small.interval = 3) formatC(x, format = "fg", decimal.mark = ",", small.mark = " ", small.interval = 3) ```