


Hi Rainer
 
Or maybe you are referring to the outer function.
I'm a newbie in R, but I recently read something about it in the pdf book named below (pages 91-2). I send to you an excerpt:
 
An introduction to R

An introduction to R
Longhow Lam

 

 
 
6.2.5 The outer function
outer function
The function outer performs an outer-product given two arrays (vectors). This can
be especially useful for evaluating a function on a grid without explicit looping. The
function has at least three input-arguments: two vectors x and y and the name of a
function that needs two or more arguments for input. For every combination of the
vector elements of x and y this function is evaluated. Some examples are given by the
code below.

outer performs an outer-product given two arrays (vectors). This can
be especially useful for evaluating a function on a grid without explicit looping. The
function has at least three input-arguments: two vectors x and y and the name of a
function that needs two or more arguments for input. For every combination of the
vector elements of x and y this function is evaluated. Some examples are given by the
code below.

x and y and the name of a
function that needs two or more arguments for input. For every combination of the
vector elements of x and y this function is evaluated. Some examples are given by the
code below.
x and y this function is evaluated. Some examples are given by the
code below.
 

x <- 1:3
y <- 1:3
z <- outer(x,y,FUN="-")
z
[,1] [,2] [,3]
[1,] 0 -1 -2
[2,] 1 0 -1
[3,] 2 1 0
x <- c("A", "B", "C", "D")
y <- 1:9
z <- outer(x, y, paste, sep = "")
z
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
[1,] "A1" "A2" "A3" "A4" "A5" "A6" "A7" "A8" "A9"
[2,] "B1" "B2" "B3" "B4" "B5" "B6" "B7" "B8" "B9"
[3,] "C1" "C2" "C3" "C4" "C5" "C6" "C7" "C8" "C9"
[4,] "D1" "D2" "D3" "D4" "D5" "D6" "D7" "D8" "D9"

z
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
[1,] "A1" "A2" "A3" "A4" "A5" "A6" "A7" "A8" "A9"
[2,] "B1" "B2" "B3" "B4" "B5" "B6" "B7" "B8" "B9"
[3,] "C1" "C2" "C3" "C4" "C5" "C6" "C7" "C8" "C9"
[4,] "D1" "D2" "D3" "D4" "D5" "D6" "D7" "D8" "D9"
z <- outer(x, y, paste, sep = "")
z
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
[1,] "A1" "A2" "A3" "A4" "A5" "A6" "A7" "A8" "A9"
[2,] "B1" "B2" "B3" "B4" "B5" "B6" "B7" "B8" "B9"
[3,] "C1" "C2" "C3" "C4" "C5" "C6" "C7" "C8" "C9"
[4,] "D1" "D2" "D3" "D4" "D5" "D6" "D7" "D8" "D9"


-----Original Message-----
From: David L Lorenz <lorenz@usgs.gov>
To: Rainer M Krug <r.m.krug@gmail.com>
Cc: r-help@r-project.org
Sent: Fri, Mar 11, 2011 9:31 am
Subject: Re: [R] How to get all combinations between two character vectors?


Rainer,
 The are probably lots of ways, I'd use
levels(interaction(c("a", "b"), c('x', 'y'), sep=''))
  Dave
>Hi

I know there is a function - I have used it before - but I always forget
what it is called...

I need the combination of two character vectors, i.e:

x <- c("a", "b")
y <- c("x", "y")

z <- THEFUNCTION(x, y)

z == c("ax", "ay", "bx", "by")

I promise I will write the name of the function on my desk!

Thanks,

Rainer
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