| Re: Removing (or replacing) substrings in a string array [message #87283 is a reply to message #87262] |
Wed, 22 January 2014 14:57   |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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On 1/22/14, 7:13 AM, Mats Löfdahl wrote:
> Say I have a string array where each string may or may not begin with
> a dot (".") and may or may not end with a dot. What is an efficient
> (non-loop?) way of removing those dots in IDL 7?
>
> The reason I specify IDL 7 is that I realize this could be done with
> strsplit in IDL 8 but in IDL 7 straplit does not support string
> arrays.
>
>
> Alternatively, if I could make it so those dots are not there in the
> first place, that's even better. What I'm trying to do it to parse an
> array of strings, where the fields are separated by dots but I cannot
> identify the substrings by their position. What I can do is to
> identify them with regular expressions because they all have
> different forms. And stregex supports string arrays also in IDL 7.
>
> So I can do something like
> strmid(stregex(strlist,'\.[0-9]{5}\.',/extr),1,5) if I know I have a
> five-digit number surrounded by dots. I remove the dots with the
> strmid command.
>
> But any field can also be first or last, so to find it I need to do
> stregex(strlist,'(\.|^)[0-9]{5}(\.|$)',/extr). But then one of the
> dots will be missing in those cases when the field really is first or
> last, so the simple strmid operation does not work.
>
> And some fields can have variable lengths but be identified by an
> initial character, so I could find it with something like
> stregex(strlist,'(\.|^)f[+-][0-9]+(\.|$)',/extr). In this case strmid
> does not work even when there is a dot at the end, because I don't
> know its position.
>
> Would be great if I could tell stregex to return everything but the
> dots (if present) but I don't know if that is possible. Can't you do
> something like that with regular expressions in the shell? Or was it
> in elisp?
>
>
> I wanted to educate myself and went looking for “Making Regular
> Expressions Your Friends” by Mike Galloy but the links seem to be
> dead in http://michaelgalloy.com/2006/06/11/regular-expressions.html
> and the link in
> http://www.exelisvis.com/docs/Learning_About_Regular_E.html leads to
> a page telling me that "The mgunit project site has moved to Github"
> and when I follow the provided link to github I can't find the
> document.
>
>
> Hmmm... I guess if I substitute '.'+strlist+'.' for strlist in all
> stregex calls I don't have to worry about the case where there are no
> dots. But that seems not so elegant and it still does not solve the
> problem with unknown lengths.
>
Check out MG_STREPLACE:
https://github.com/mgalloy/mglib/blob/master/src/strings/mg_ streplace.pro
I have that "Making Regular Expressions Your Friends" article here
somewhere too. I will update the link on my website and post here when I
find it. Have to run now...
Mike
--
Michael Galloy
www.michaelgalloy.com
Modern IDL: A Guide to IDL Programming (http://modernidl.idldev.com)
Research Mathematician
Tech-X Corporation
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