[R] replace values in vector from a replacement table

[jim holtman]

try this:

> (x <- rep(letters,2))
 [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p"
"q" "r" "s" "t" "u" "v" "w"
[24] "x" "y" "z" "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m"
"n" "o" "p" "q" "r" "s" "t"
[47] "u" "v" "w" "x" "y" "z"
> values <- c("aa", "a", "b", NA, "d", "zz")
> repl <- c("aa", "A", "B", NA, "D", "zz")
> (repl.tab <- cbind(values, repl))
     values repl
[1,] "aa"   "aa"
[2,] "a"    "A"
[3,] "b"    "B"
[4,] NA     NA
[5,] "d"    "D"
[6,] "zz"   "zz"
> indx <- match(x, repl.tab[, 1], nomatch = 0)
> x[indx != 0] <- repl.tab[indx, 2]
> x
 [1] "A" "B" "c" "D" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p"
"q" "r" "s" "t" "u" "v" "w"
[24] "x" "y" "z" "A" "B" "c" "D" "e" "f" "g" "h" "i" "j" "k" "l" "m"
"n" "o" "p" "q" "r" "s" "t"
[47] "u" "v" "w" "x" "y" "z"
>
>


On Mon, Jul 30, 2012 at 11:53 AM, Liviu Andronic <landronimirc at gmail.com> wrote:
> Dear all
> I've got stuck when trying to replace values in a vector by selecting
> replacements from a replacement table. I'm trying to use only base
> functions. Here's a dummy example:
>> (x <- rep(letters,2))
>  [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p"
> "q" "r" "s" "t" "u" "v"
> [23] "w" "x" "y" "z" "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l"
> "m" "n" "o" "p" "q" "r"
> [45] "s" "t" "u" "v" "w" "x" "y" "z"
>> values <- c("aa", "a", "b", NA, "d", "zz")
>> repl <- c("aa", "A", "B", NA, "D", "zz")
>> (repl.tab <- cbind(values, repl))
>      values repl
> [1,] "aa"   "aa"
> [2,] "a"    "A"
> [3,] "b"    "B"
> [4,] NA     NA
> [5,] "d"    "D"
> [6,] "zz"   "zz"
>
>
> Now I can easily compute all four combinations of 'match' and '%in%':
>> (ind <- match(x, repl.tab[ ,1]))
>  [1]  2  3 NA  5 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
> NA NA NA NA  2  3 NA
> [30]  5 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
>> (ind <- match(repl.tab[ ,1], x))
> [1] NA  1  2 NA  4 NA
>> (ind <- x %in% repl.tab[ ,1])
>  [1]  TRUE  TRUE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> FALSE FALSE FALSE
> [15] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> FALSE  TRUE  TRUE
> [29] FALSE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> FALSE FALSE FALSE
> [43] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
>> (ind <- repl.tab[ ,1] %in% x)
> [1] FALSE  TRUE  TRUE FALSE  TRUE FALSE
>
>
> But how do I actually proceed to obtain the following vector?  Can it
> be done without an explicit apply() or loop?
>> res
>  [1] "A" "B" "c" "D" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p"
> "q" "r" "s" "t" "u" "v"
> [23] "w" "x" "y" "z" "A" "B" "c" "D" "e" "f" "g" "h" "i" "j" "k" "l"
> "m" "n" "o" "p" "q" "r"
> [45] "s" "t" "u" "v" "w" "x" "y" "z"
>
>
> Regards
> Liviu
>
>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.