| string manipulation [message #23898] |
Mon, 26 February 2001 14:34  |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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I have been thinking about the following problem, but have been pretty
frustrated.
I have input keyword/value strings of the following form. People may
recognize this from a FITS file.
TTYPE2 = 'X1LSpecPcu0' / X1LSpecPcu0 : Histogram
TUNIT2 = 'count '
1CTYP2 = 'CHANNEL '
1CPIX2 = '0~4,5:53,(54~135;2),(136~237;3),(238~249;4),250~255'
12CD2A = 1.25
^name^^ ^value^^^^^^^
All of the keyword names have a trailing "2" which indicates that they
are describing column number 2 in a FITS table. Note that in the name
"12CD2A", only the *final* 2 refers to the column number.
The interesting question happens when I want to change the column
number, say from "2" to "50". Is there a straightforward way to do
this in "vectoral" sort of way?
I am able to find the string positions of the 2's, so that's not
really a problem. I do this by making a byte array of the strings,
and blanking out any alphabetic characters and any leading numeric
characters. Here I appreciate STRPOS is (partially) vectorized.
However, when it comes to resubstituting the "50" back in, that's when
I get stymied. This is primarily because STRMID and STRPUT are not
vectorized at all. Well STRMID *is* vectorized, but not with a sane
behavior. For example, what I'd like to do is:
NEWKEY = STRMID(KEY,0,P1) + '50' + STRMID(KEY,P2,100)
Where KEY, P1, and P2 are vectors. Obviously this doesn't work. Any
ideas?
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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| Re: string manipulation [message #23959 is a reply to message #23898] |
Tue, 27 February 2001 16:35  |
John-David T. Smith
Messages: 384
Registered: January 2000
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Senior Member |
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Mark Hadfield wrote:
>
> "JD Smith" <jdsmith@astro.cornell.edu> wrote in message
> news:3A9C2CF5.F632B1AF@astro.cornell.edu...
>> [...]
>> new=strmid(key,0,transpose(p1))+'50'+strmid(key,tranpose(p2) )
>>
>> The key is putting the threading vector on its head, as a column
>> vector.
>
> Aaaaagh! The major reason I hate Matlab is all the "Have I got a row vector
> or a column vector?" rubbish! I feel like picking it up & shaking it &
> saying, "No, it's not a matrix, it's not a column vector, it's not a row
> vector, it's just a list of numbers. It's not dimensioned (n,1) and it's not
> dimensioned (1,n), it's dimensioned (n). You can print it vertically, you
> can print it horizontally, I don't care, it's just a list of numbers!"
>
> And now JD shows us how to confuse ourselves with row vectors and column
> vectors in IDL! As if HISTOGRAM wasn't enough. JD, I call down a curse on
> you, and your children, and your children's chil.....[falls from chair in
> paroxysm of rage]
Good on ya. I aim to please.
JD
P.S. The many ways to make column vectors:
IDL> cv=[[1],[2],[3]]
or
IDL> cv=rotate([1,2,3],1)
or
IDL> cv=transpose([1,2,3])
or
IDL> cv=array[0,*]
or
IDL> cv=reform([1,2,3],1,3)
or
IDL> cv=[1,2,3]##1
or
IDL> cv=1#[1,2,3]
or
...
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| Re: string manipulation [message #23963 is a reply to message #23898] |
Tue, 27 February 2001 15:02 |
Mark Hadfield
Messages: 783
Registered: May 1995
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Senior Member |
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"JD Smith" <jdsmith@astro.cornell.edu> wrote in message
news:3A9C2CF5.F632B1AF@astro.cornell.edu...
> [...]
> new=strmid(key,0,transpose(p1))+'50'+strmid(key,tranpose(p2) )
>
> The key is putting the threading vector on its head, as a column
> vector.
Aaaaagh! The major reason I hate Matlab is all the "Have I got a row vector
or a column vector?" rubbish! I feel like picking it up & shaking it &
saying, "No, it's not a matrix, it's not a column vector, it's not a row
vector, it's just a list of numbers. It's not dimensioned (n,1) and it's not
dimensioned (1,n), it's dimensioned (n). You can print it vertically, you
can print it horizontally, I don't care, it's just a list of numbers!"
And now JD shows us how to confuse ourselves with row vectors and column
vectors in IDL! As if HISTOGRAM wasn't enough. JD, I call down a curse on
you, and your children, and your children's chil.....[falls from chair in
paroxysm of rage]
---
Mark Hadfield
m.hadfield@niwa.cri.nz http://katipo.niwa.cri.nz/~hadfield
National Institute for Water and Atmospheric Research
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| Re: string manipulation [message #23965 is a reply to message #23898] |
Tue, 27 February 2001 14:40 |
John-David T. Smith
Messages: 384
Registered: January 2000
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Senior Member |
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Wayne Landsman wrote:
>
> In article <on66hxm5tk.fsf@cow.physics.wisc.edu>, craigmnet@cow.physics.wisc.edu writes...
>> This is primarily because STRMID and STRPUT are not
>> vectorized at all. Well STRMID *is* vectorized, but not with a sane
>> behavior. For example, what I'd like to do is:
>>
>> NEWKEY = STRMID(KEY,0,P1) + '50' + STRMID(KEY,P2,100)
>> NEWKEY = STRMID(KEY,0,P1) + '50' + STRMID(KEY,P2,100)
>>
>> Where KEY, P1, and P2 are vectors. Obviously this doesn't work. Any
>> ideas?
>
> The problem when STRMID was vectorized for V5.3 was that it was made *too*
> powerful -- it handles simultaneously both extraction from multiple strings
> and multiple extractions from a single string. In practice, I think the
> first situation -- extraction from multiple strings -- is far more common, but
> has an ugly syntax in the current STRMID implementation. Here is how one
> does the example above.
>
> N = N_elements(KEY)
> NEWKEY = STRMID(KEY,INTARR(1,N),REFORM(P1,1,N)) + '50' + $
> STRMID(KEY,REFORM(P2,1,N), REPLICATE(100,1,N) )
>
> I have thought about writing a simple wrapper around STRMID (say STRMIDV) that
> would have a simpler syntax for the case of single extractions from
> multiple strings.
Aha! Where there's a will... Pavel, rejoin your faith.
A bit of a refinement, for the lazy among us:
new=strmid(key,0,transpose(p1))+'50'+strmid(key,tranpose(p2) )
The key is putting the threading vector on its head, as a column
vector. Another simplification arrives from strmid's willingness to
loop back over vectors which are too short (like the scalar 0), and to
extract all the way to the end of a string, if no length is specified.
Row vectors are interpreted as multiple places in each given string to
operate. Power, with a price.
Note that an even easier notation appears if you have p1 and p2 as
columns in an array, e.g.:
IDL> p=[ [1,5], [2,6], [3,6], [4,8] ]
then you can simply use the relatively clean:
new=strmid(key,0,p[0,*])+'50'+strmid(key,p[1,*])
Here is a perfect case of where IDL's notion of keeping leading
dimensions of size 1 is critical. Note that p[0,*] are lengths, and
p[1,*] are subscripts.
This also works quite well for p1 and p2 not the same length as key, or
each other.
JD
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| Re: string manipulation [message #23966 is a reply to message #23898] |
Tue, 27 February 2001 13:29 |
landsman
Messages: 93
Registered: August 1991
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Member |
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In article <on66hxm5tk.fsf@cow.physics.wisc.edu>, craigmnet@cow.physics.wisc.edu writes...
> This is primarily because STRMID and STRPUT are not
> vectorized at all. Well STRMID *is* vectorized, but not with a sane
> behavior. For example, what I'd like to do is:
>
> NEWKEY = STRMID(KEY,0,P1) + '50' + STRMID(KEY,P2,100)
> NEWKEY = STRMID(KEY,0,P1) + '50' + STRMID(KEY,P2,100)
>
> Where KEY, P1, and P2 are vectors. Obviously this doesn't work. Any
> ideas?
The problem when STRMID was vectorized for V5.3 was that it was made *too*
powerful -- it handles simultaneously both extraction from multiple strings
and multiple extractions from a single string. In practice, I think the
first situation -- extraction from multiple strings -- is far more common, but
has an ugly syntax in the current STRMID implementation. Here is how one
does the example above.
N = N_elements(KEY)
NEWKEY = STRMID(KEY,INTARR(1,N),REFORM(P1,1,N)) + '50' + $
STRMID(KEY,REFORM(P2,1,N), REPLICATE(100,1,N) )
I have thought about writing a simple wrapper around STRMID (say STRMIDV) that
would have a simpler syntax for the case of single extractions from
multiple strings.
--Wayne Landsman landsman@mpb.gsfc.nasa.gov
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| Re: string manipulation [message #23999 is a reply to message #23925] |
Thu, 01 March 2001 11:54 |
Pavel A. Romashkin
Messages: 531
Registered: November 2000
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Senior Member |
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"Kenneth P. Bowman" wrote:
>
> No, but I expect someone could whip up an object to *render* a virtual
> pint of beer. But wait, would that be hardware or software rendering?
Just make sure it works on my Mac... and does not render a Budweiser. I
don't care whether it uses OpenGL to open the bottle or a hardware tool.
Pavel
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