Here's what you did:
> gsub("x1", "i1", "x1 + x2 + x10 + xx1")
[1] "i1 + x2 + i10 + xi1"The following worked for me to just change "x1" to "i1", while leaving alone any larger "word" that contains "x1":
> gsub("\\bx1\\b", "i1", "x1 + x2 + x10 + xx1")
[1] "i1 + x2 + x10 + xx1"
>Note that the backslash must be escaped itself to get past the R lexical analyser, which is independent of the regexp processor. What the regexp processor sees is just a single backslash.
For more on this, look for perl documentation of regular expressions. Be aware that to use full perl regexps, you must supply the perl=T argument to gsub(). Also note that "\b" seems to be part of the most basic regular expression language in R; it even works with extended=F:
> gsub("\\bx1\\b", "i1", "x1 + x2 + x10 + xx1", perl=T)
[1] "i1 + x2 + x10 + xx1"
> gsub("\\bx1\\b", "i1", "x1 + x2 + x10 + xx1", perl=F)
[1] "i1 + x2 + x10 + xx1"
> gsub("\\bx1\\b", "i1", "x1 + x2 + x10 + xx1", perl=F, ext=F)
[1] "i1 + x2 + x10 + xx1"
>(I assumed the fact that you have a matrix of strings is not relevant.)
Hope this helps,
Tony Plate
At Wednesday 09:07 PM 10/27/2004, Kevin Wang wrote:
Hi,
Suppose I've got a matrix, and the first few elements look like "x1 + x3 + x4 + x5 + x1:x3 + x1:x4" "x1 + x2 + x3 + x5 + x1:x2 + x1:x5" "x1 + x3 + x4 + x5 + x1:x3 + x1:x5" and so on (have got terms from x1 ~ x14).
If I want to replace all the x1 with i7, all x2 with i14, all x3 with i13, for example. Is there an easy way?
I tried to put what I want to replace in a vector, like: repl = c("i7", "i14", "i13", "d2", "i8", "i5", "i6", "i3", "A", "i9", "i2", "i4", "i15", "i21") and have another vector, say: > orig [1] "x1" "x2" "x3" "x4" "x5" "x6" "x7" "x8" "x9" "x10" [11] "x11" "x12" "x13" "x14"
Then I tried something like gsub(orig, repl, mat) ## mat is the name of my matrix
but it didn't work *_*.....it would replace terms like x10 with i70.
(I know it may be an easy question...but I haven't done much regular expression)
Cheers,
Kevin
-------------------------------- Ko-Kang Kevin Wang PhD Student Centre for Mathematics and its Applications Building 27, Room 1004 Mathematical Sciences Institute (MSI) Australian National University Canberra, ACT 0200 Australia
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