Colon Operator

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Description

Generate regular sequences.

Usage

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from:to
   a:b

Arguments

from

starting value of sequence.

to

(maximal) end value of the sequence.

a, b

factors of the same length.

Details

The binary operator : has two meanings: for factors a:b is equivalent to interaction(a, b) (but the levels are ordered and labelled differently).

For other arguments from:to is equivalent to seq(from, to), and generates a sequence from from to to in steps of 1 or -1. Value to will be included if it differs from from by an integer up to a numeric fuzz of about 1e-7. Non-numeric arguments are coerced internally (hence without dispatching methods) to numeric—complex values will have their imaginary parts discarded with a warning.

Value

For numeric arguments, a numeric vector. This will be of type integer if from is integer-valued and the result is representable in the R integer type, otherwise of type "double" (aka mode "numeric").

For factors, an unordered factor with levels labelled as la:lb and ordered lexicographically (that is, lb varies fastest).

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
(for numeric arguments: S does not have : for factors.)

See Also

seq (a generalization of from:to).

As an alternative to using : for factors, interaction.

For : used in the formal representation of an interaction, see formula.

Examples

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1:4
pi:6 # real
6:pi # integer

f1 <- gl(2, 3); f1
f2 <- gl(3, 2); f2
f1:f2 # a factor, the "cross"  f1 x f2

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