Cross Tabulation and Table Creation (original) (raw)

table {base}	R Documentation

Description

table uses cross-classifying factors to build a contingency table of the counts at each combination of factor levels.

Usage

table(...,
      exclude = if (useNA == "no") c(NA, NaN),
      useNA = c("no", "ifany", "always"),
      dnn = list.names(...), deparse.level = 1)

as.table(x, ...)
is.table(x)

## S3 method for class 'table'
as.data.frame(x, row.names = NULL, ...,
              responseName = "Freq", stringsAsFactors = TRUE,
              sep = "", base = list(LETTERS))

Arguments

...	one or more objects which can be interpreted as factors (including numbers or character strings), or a list (such as a data frame) whose components can be so interpreted. (For as.table, arguments passed to specific methods; for as.data.frame, unused.)
exclude	levels to remove for all factors in .... If it does not contain NA and useNA is not specified, it implies useNA = "ifany". See ‘Details’ for its interpretation for non-factor arguments.
useNA	whether to include NA values in the table. See ‘Details’. Can be abbreviated.
dnn	the names to be given to the dimensions in the result (the_dimnames names_).
deparse.level	controls how the default dnn is constructed. See ‘Details’.
x	an arbitrary R object, or an object inheriting from class"table" for the as.data.frame method. Note thatas.data.frame.table(x, *) may be called explicitly for non-table x for “reshaping” arrays.
row.names	a character vector giving the row names for the data frame.
responseName	the name to be used for the column of table entries, usually counts.
stringsAsFactors	logical: should the classifying factors be returned as factors (the default) or character vectors?
sep, base	passed to provideDimnames.

Details

If the argument dnn is not supplied, the internal functionlist.names is called to compute the ‘dimname names’ as follows: If ... is one list with its own [names](../../base/help/names.html)(), these names are used. Otherwise, if the arguments in ... are named, those names are used. For the remaining arguments, deparse.level = 0 gives an empty name,deparse.level = 1 uses the supplied argument if it is a symbol, and deparse.level = 2 will deparse the argument.

Only when exclude is specified (i.e., not by default) and non-empty, will table potentially drop levels of factor arguments.

useNA controls if the table includes counts of NAvalues: the allowed values correspond to never ("no"), only if the count is positive ("ifany") and even for zero counts ("always"). Note the somewhat “pathological” case of two different kinds ofNAs which are treated differently, depending on bothuseNA and exclude, see d.patho in the ‘Examples:’ below.

Both exclude and useNA operate on an “all or none” basis. If you want to control the dimensions of a multiway table separately, modify each argument using [factor](../../base/help/factor.html) or[addNA](../../base/help/addNA.html).

Non-factor arguments a are coerced via factor(a, exclude=exclude). Since R 3.4.0, care is taken not to count the excluded values (where they were included in the NAcount, previously).

The summary method for class "table" (used for objects created by table or [xtabs](../../stats/html/xtabs.html)) which gives basic information and performs a chi-squared test for independence of factors (note that the function [chisq.test](../../stats/html/chisq.test.html) currently only handles 2-d tables).

Value

table() returns a contingency table, an object of class "table", an array of integer values. Note that unlike S the result is always an [array](../../base/help/array.html), a 1D array if one factor is given.

as.table and is.table coerce to and test for contingency table, respectively.

The as.data.frame method for objects inheriting from class"table" can be used to convert the array-based representation of a contingency table to a data frame containing the classifying factors and the corresponding entries (the latter as component named by responseName). This is the inverse of [xtabs](../../stats/html/xtabs.html).

References

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

Examples

require(stats) # for rpois and xtabs
## Simple frequency distribution
table(rpois(100, 5))
## Check the design:
with(warpbreaks, table(wool, tension))
table(state.division, state.region)

# simple two-way contingency table
with(airquality, table(cut(Temp, quantile(Temp)), Month))

a <- letters[1:3]
table(a, sample(a))                    # dnn is c("a", "")
table(a, sample(a), dnn = NULL)        # dimnames() have no names
table(a, sample(a), deparse.level = 0) # dnn is c("", "")
table(a, sample(a), deparse.level = 2) # dnn is c("a", "sample(a)")

## xtabs() <-> as.data.frame.table() :
UCBAdmissions ## already a contingency table
DF <- as.data.frame(UCBAdmissions)
class(tab <- xtabs(Freq ~ ., DF)) # xtabs & table
## tab *is* "the same" as the original table:
all(tab == UCBAdmissions)
all.equal(dimnames(tab), dimnames(UCBAdmissions))

a <- rep(c(NA, 1/0:3), 10)
table(a)                 # does not report NA's
table(a, exclude = NULL) # reports NA's
b <- factor(rep(c("A","B","C"), 10))
table(b)
table(b, exclude = "B")
d <- factor(rep(c("A","B","C"), 10), levels = c("A","B","C","D","E"))
table(d, exclude = "B")
print(table(b, d), zero.print = ".")

## NA counting:
is.na(d) <- 3:4
d. <- addNA(d)
d.[1:7]
table(d.) # ", exclude = NULL" is not needed
## i.e., if you want to count the NA's of 'd', use
table(d, useNA = "ifany")

## "pathological" case:
d.patho <- addNA(c(1,NA,1:2,1:3))[-7]; is.na(d.patho) <- 3:4
d.patho
## just 3 consecutive NA's ? --- well, have *two* kinds of NAs here :
as.integer(d.patho) # 1 4 NA NA 1 2
##
## In R >= 3.4.0, table() allows to differentiate:
table(d.patho)                   # counts the "unusual" NA
table(d.patho, useNA = "ifany")  # counts all three
table(d.patho, exclude = NULL)   #  (ditto)
table(d.patho, exclude = NA)     # counts none

## Two-way tables with NA counts. The 3rd variant is absurd, but shows
## something that cannot be done using exclude or useNA.
with(airquality,
   table(OzHi = Ozone > 80, Month, useNA = "ifany"))
with(airquality,
   table(OzHi = Ozone > 80, Month, useNA = "always"))
with(airquality,
   table(OzHi = Ozone > 80, addNA(Month)))

[Package _base_ version 4.6.0 Index]