Encode in a Common Format

Format an R object for pretty printing.

print, character
format(x, ...)
"format"(x, trim = FALSE, digits = NULL, nsmall = 0L, justify = c("left", "right", "centre", "none"), width = NULL, na.encode = TRUE, scientific = NA, big.mark = "", big.interval = 3L, small.mark = "", small.interval = 5L, decimal.mark = ".", zero.print = NULL, drop0trailing = FALSE, ...)
"format"(x, ..., justify = "none")
"format"(x, ...)
"format"(x, width = 12, ...)
any R object (conceptually); typically numeric.
logical; if FALSE, logical, numeric and complex values are right-justified to a common width: if TRUE the leading blanks for justification are suppressed.
how many significant digits are to be used for numeric and complex x. The default, NULL, uses getOption("digits"). This is a suggestion: enough decimal places will be used so that the smallest (in magnitude) number has this many significant digits, and also to satisfy nsmall. (For the interpretation for complex numbers see signif.)
the minimum number of digits to the right of the decimal point in formatting real/complex numbers in non-scientific formats. Allowed values are 0 <= nsmall="" <="20.
should a character vector be left-justified (the default), right-justified, centred or left alone.
default method: the minimum field width or NULL or 0 for no restriction.

AsIs method: the maximum field width for non-character objects. NULL corresponds to the default 12.

logical: should NA strings be encoded? Note this only applies to elements of character vectors, not to numerical, complex nor logical NAs, which are always encoded as "NA".
Either a logical specifying whether elements of a real or complex vector should be encoded in scientific format, or an integer penalty (see options("scipen")). Missing values correspond to the current default penalty.
further arguments passed to or from other methods.
big.mark, big.interval, small.mark, small.interval, decimal.mark, zero.print, drop0trailing
used for prettying (longish) numerical and complex sequences. Passed to prettyNum: that help page explains the details.

format is a generic function. Apart from the methods described here there are methods for dates (see format.Date), date-times (see format.POSIXct)) and for other classes such as format.octmode and format.dist. formats the data frame column by column, applying the appropriate method of format for each column. Methods for columns are often similar to as.character but offer more control. Matrix and data-frame columns will be converted to separate columns in the result, and character columns (normally all) will be given class "AsIs".

format.factor converts the factor to a character vector and then calls the default method (and so justify applies).

format.AsIs deals with columns of complicated objects that have been extracted from a data frame. Character objects are passed to the default method (and so width does not apply). Otherwise it calls toString to convert the object to character (if a vector or list, element by element) and then right-justifies the result.

Justification for character vectors (and objects converted to character vectors by their methods) is done on display width (see nchar), taking double-width characters and the rendering of special characters (as escape sequences, including escaping backslash but not double quote: see print.default) into account. Thus the width is as displayed by print(quote = FALSE) and not as displayed by cat. Character strings are padded with blanks to the display width of the widest. (If na.encode = FALSE missing character strings are not included in the width computations and are not encoded.)

Numeric vectors are encoded with the minimum number of decimal places needed to display all the elements to at least the digits significant digits. However, if all the elements then have trailing zeroes, the number of decimal places is reduced until nsmall is reached or at least one element has a non-zero final digit; see also the argument documentation for big.*, small.* etc, above. See the note in print.default about digits >= 16.

Raw vectors are converted to their 2-digit hexadecimal representation by as.character. The internal code respects the option getOption("OutDec") for the ‘decimal mark’, so if this is set to something other than "." then it takes precedence over argument decimal.mark.


An object of similar structure to x containing character representations of the elements of the first argument x in a common format, and in the current locale's encoding.For character, numeric, complex or factor x, dims and dimnames are preserved on matrices/arrays and names on vectors: no other attributes are copied.If x is a list, the result is a character vector obtained by applying format.default(x, ...) to each element of the list (after unlisting elements which are themselves lists), and then collapsing the result for each element with paste(collapse = ", "). The defaults in this case are trim = TRUE, justify = "none" since one does not usually want alignment in the collapsed strings.


Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also indicates how an atomic vector would be formatted.

formatC, paste, as.character, sprintf, print, prettyNum, toString, encodeString.

  • format
  • format.AsIs
  • format.default
  • format.factor
library(base) format(1:10) format(1:10, trim = TRUE) zz <- data.frame("(row names)"= c("aaaaa", "b"), check.names = FALSE) format(zz) format(zz, justify = "left") ## use of nsmall format(13.7) format(13.7, nsmall = 3) format(c(6.0, 13.1), digits = 2) format(c(6.0, 13.1), digits = 2, nsmall = 1) ## use of scientific format(2^31-1) format(2^31-1, scientific = TRUE) ## a list z <- list(a = letters[1:3], b = (-pi+0i)^((-2:2)/2), c = c(1,10,100,1000), d = c("a", "longer", "character", "string"), q = quote( a + b ), e = expression(1+x)) ## can you find the "2" small differences? (f1 <- format(z, digits = 2)) (f2 <- format(z, digits = 2, justify = "left", trim = FALSE)) f1 == f2 ## 2 FALSE, 4 TRUE
Documentation reproduced from package base, version 3.1.3, License: Part of R 3.1.3

Community examples at Jan 17, 2017 base v3.3.2

By default, `format()` adds leading spaces so that all values have the same length. Setting `trim = TRUE` turns this off. ```{r} x <- 10 ^ (0:4) format(x) format(x, trim = TRUE) ``` `digits` sets the number of significant digits. ```{r} x2 <- c(0, 0.1, 0.12, 0.123, 0.1234) format(x2, digits = 3) ``` Actually, it sets significant digits for the smallest (in magnitude) value, so if you have orders of magnitude range, treat it as a suggestion and fiddle as necessary. ```{r} x <- 10 ^ (0:4) x2 <- c(0, 0.1, 0.12, 0.123, 0.1234) format(x + x2, digits = 3) ``` `digits` can also be useful for examining floating point rounding errors. ```{r} format(sqrt(2) * sqrt(2) - 2, digits = 22) ``` `nsmall` gives the minimum number of decimal places. ```{r} x <- 10 ^ (0:4) x2 <- c(0, 0.1, 0.12, 0.123, 0.1234) format(x + x2, nsmall = 3) ``` You can use `digits` and `nsmall` together; the result has enough digits to satisfy the sig digs and the d.p. criteria. ```{r} x <- 10 ^ (0:4) x2 <- c(0, 0.1, 0.12, 0.123, 0.1234) format(x + x2, digits = 5, nsmall = 1) format(x + x2, digits = 1, nsmall = 5) ``` `justify` lets you enforce left/right/centre justification on character vectors. It has no effect when the input is a number. ```{r} x <- 10 ^ (0:4) format(x, justify = "centre") # does nothing format(format(x, trim = TRUE), justify = "left") format(format(x, trim = TRUE), justify = "centre") ``` `width` pads values with leading spaces to set a minimum output width. ```{r} format(0, width = 10) format(1.2345, width = 1) # width is greater than 1 anyway ``` For objects of class `AsIs`, width sets the maximum output width. ```{r} x <- 10 ^ (0:4) format(I(x), width = 3) ``` Usually `format()` turns `NA` into `"NA"`. Setting `na.encode = FALSE` turns this behaviour off for character vectors. ```{r} format(c("abc", NA), na.encode = FALSE) format(c(1, NA), na.encode = FALSE) # no effect ``` For numeric vectors, you can turn scientific formatting on or off iwth the `scientific` argument. ```{r} format(2 ^ 31 - 1, scientific = FALSE) format(2 ^ 31 - 1, scientific = TRUE) ``` This doesn't work for integers. ```{r} format(.Machine$integer.max, scientific = TRUE) ``` There are more arguments for customising the output for written reports. See [`prettyNum()`]( for more. ```{r} format( 123456789.87654321, digits = 17, big.mark = ",", small.mark = " ", small.interval = 2 ) ``` For data frames, the arguments passed to format work on all columns. ```{r} co2 <- CO2[sample(nrow(CO2), 12), ] format(co2, justify = "left", width = 10, scientific = TRUE) ``` Factors default to left justification (in a left-to-right locale?) ```{r} f <- factor(sample(, 25, replace = TRUE)) format(f) format(f, justify = "right", width = 12) ```