| Sort without loops [message #45166] |
Wed, 17 August 2005 02:08  |
Ian Dean
Messages: 26
Registered: January 2000
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Junior Member |
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Hi All,
I have a large string array (~100000 elements) that need sorting on two
fields within each string.
e.g. array=['F;100', 'ABC;6', 'DE;2', 'DE;10', 'DE;1']
Order required is a) sort items to left of ';' followed by b) sort items
numerically to right of ';'
This would produce:
ABC;6 DE;1 DE;2 DE;10 F;100
A simple sort (sort(array)) procudes:
ABC;6 DE;1 DE;10 DE;2 F;100
The only way I've found is to conmvert the RH part to I4.4 format within a
loop and search on the new values:
......
for j=0, n_elements(array)-1 do begin
parts=strsplit(array[j], ';', /extract)
RH=string(fix(parts[1]), format='(I4.4)')
new[j]=parts[0]+RH
endfor
order=sort(new)
...
i.e
new array is F;0100 ABC;0006 DE;0002 DE;0010 DE;0001
which is then sorted correctly.
Is there a clever way of sorting on two fields like this without using a
loop. The above algorithm is faaaar slower than just using sort.
I hope I have made this as clear as mud.#
In expectation,
Ian
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| Re: Sort without loops [message #45224 is a reply to message #45166] |
Fri, 19 August 2005 08:05  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Ed Hyer writes:
> I started using IDL about 14 months ago, and now I have a Ph.D. to show
> for it. Your help has been essential to this.
> My "IDL Way" story has to do with resampling a 3d xyt grid to match a
> list of irregular samples in space and time. By using HIST_ND and
> creative array manipulation, I changed a procedure that took six+ hours
> into one that takes 30 seconds. My largest bottleneck is now loading
> the data off the disk.
Whoa! Do you remember the details. I have a guy bugging me
about this kind of thing right now!
I'll send you a template and you can write it up.
I'm pretty sure you will be famous. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: Sort without loops [message #45226 is a reply to message #45166] |
Fri, 19 August 2005 07:57 |
MarioIncandenza
Messages: 231
Registered: February 2005
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Senior Member |
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David,
I started using IDL about 14 months ago, and now I have a Ph.D. to show
for it. Your help has been essential to this.
My "IDL Way" story has to do with resampling a 3d xyt grid to match a
list of irregular samples in space and time. By using HIST_ND and
creative array manipulation, I changed a procedure that took six+ hours
into one that takes 30 seconds. My largest bottleneck is now loading
the data off the disk.
Cheers,
Edward Hyer.
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| Re: Sort without loops [message #45242 is a reply to message #45166] |
Thu, 18 August 2005 06:41 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Ian Dean writes:
> Thanks to you all it works well.
Did you happen to run a speed test on this, Ian?
I have a new section on my Tips page called "The
IDL Way". I generally don't put things on my page
that I don't understand, but I'm making a few
exceptions for JD's legerdemain. It is nice to put
at the end of the article "By using the IDL Way I
sped the algorithm up by a factor of 1,345,723."
Cheers,
David
P.S. If anyone has their favorite IDL Way story,
I'm accepting all the help I can get. :-)
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: Sort without loops [message #45243 is a reply to message #45166] |
Thu, 18 August 2005 06:28 |
Ian Dean
Messages: 26
Registered: January 2000
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Junior Member |
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Thanks to you all it works well.
"Ian Dean" <Ian.d.dean@baesystems.com> wrote in message
news:4302fc84$1_1@glkas0286.greenlnk.net...
> Hi All,
> I have a large string array (~100000 elements) that need sorting on
two
> fields within each string.
>
> e.g. array=['F;100', 'ABC;6', 'DE;2', 'DE;10', 'DE;1']
>
> Order required is a) sort items to left of ';' followed by b) sort items
> numerically to right of ';'
> This would produce:
> ABC;6 DE;1 DE;2 DE;10 F;100
>
> A simple sort (sort(array)) procudes:
> ABC;6 DE;1 DE;10 DE;2 F;100
>
> The only way I've found is to conmvert the RH part to I4.4 format within a
> loop and search on the new values:
> ......
> for j=0, n_elements(array)-1 do begin
> parts=strsplit(array[j], ';', /extract)
> RH=string(fix(parts[1]), format='(I4.4)')
> new[j]=parts[0]+RH
> endfor
> order=sort(new)
> ...
> i.e
> new array is F;0100 ABC;0006 DE;0002 DE;0010 DE;0001
> which is then sorted correctly.
>
> Is there a clever way of sorting on two fields like this without using a
> loop. The above algorithm is faaaar slower than just using sort.
>
> I hope I have made this as clear as mud.#
>
> In expectation,
> Ian
>
>
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