On Jan 27, 2007, at 3:41 PM, Phillimore, Albert wrote:
Dear R Users,
I am trying to users gsub to remove multiple cases of square
brackets and their different contents in a character string. A
sample of such a string is shown below. However, I am having great
difficulty understanding regexp syntax. Any help is greatly
appreciated.
Ally
tree STATE_286000 [lnP=-12708.453945423369] = [R] ((15
[rate=0.009761226401396686]:7.040851727747465,17
[rate=0.011500289631135564]:7.040851727747465)
[rate=0.010986570567484494]:2.257049446900292,(18
[rate=0.009123432243563103]:2.461289418776003,19
[rate=0.00981822432115329]:2.461289418776003)
Is this what you want? I tend to prefer perl regular expressions:
str - tree STATE_286000 [lnP=-12708.453945423369] = [R]
((15[rate=0.009761226401396686]:7.040851727747465,17
[rate=0.011500289631135564]:7.040851727747465)
[rate=0.010986570567484494]:2.257049446900292,(18
[rate=0.009123432243563103]:2.461289418776003,19
[rate=0.00981822432115329]:2.461289418776003)
gsub(\\[[^\\]]+\\],,str, perl=T)
[1] tree STATE_286000 =
((15:7.040851727747465,17:7.040851727747465):2.257049446900292,
(18:2.461289418776003,19:2.461289418776003)
As an explanation, \\[ and \\] match the two square brackets you
want. We need to escape the brackets with the backslashes because
they have a special meaning in perl regular expressions.
In perl regexps, [] stands for match a single character that
is like what we have in the For instance [ab] will match an a or
a b. [a-z] will match all lowercase characters. A ^ as a first
character in there means match all but what follows. for instance
[^a-z] means match anything but lowercase characters. So [^\\]] means
match any character but a closing bracket.
Finally the plus sign afterwards means: match at least one. So [^\\]]
+ means match any sequence of characters that does not contain a
closing bracket. So the whole thing now matches an opening bracket,
followed by all characters until a corresponding closing bracket.
This will not work if you have nested pairs of brackets, [like [so]].
That is a tad more delicate, and we can discuss it if you really need
to deal with it.
Haris
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