| Concatenate elements of string array [message #16657] |
Mon, 09 August 1999 00:00  |
kluegel
Messages: 11
Registered: February 1999
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Junior Member |
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Does anyone out there have a clever idea on how to
concatenate all elements of a one dimensional array
of strings? Of course, explicit looping is the
obvious way to do it, but approaches using array
manipulation tend to be more efficient. Any
array-based approaches out there?
Thanks for any ideas.
-- Tom Kluegel
Los Alamos National Lab
Los Alamos, New Mexico, USA
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| Re: Concatenate elements of string array [message #16712 is a reply to message #16657] |
Thu, 12 August 1999 00:00  |
kluegel
Messages: 11
Registered: February 1999
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Junior Member |
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In article <7othpe$cin$1@nnrp1.deja.com>,
kluegel@lanl.gov wrote:
> result = STRING( string_array, FORMAT='(16(16384(16384A)))' )
One gotcha still appears to be nul characters, which gives weird
behavior. This is likely because IDL is implemented in C/C++ which uses
nul terminated strings. So we still have to impose the rule that no
nul characters are allowed in any strings in the string array.
-- Tom Kluegel
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| Re: Concatenate elements of string array [message #16724 is a reply to message #16657] |
Thu, 12 August 1999 00:00 |
kluegel
Messages: 11
Registered: February 1999
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Junior Member |
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In article <37B1730A.41C6@icg.tu-graz.ac.SIG>,
Ruhaltinger Norbert <norbertr@icg.tu-graz.ac.SIG> wrote:
> string can be used like sprintf in C
> You have to create the Format specification on the fly
>
> IDL> string_array=['one ','string ','split ',$
> 'into ','many ','array elements']
> IDL> help,string_array & print,string_array
> STRING_ARRAY STRING = Array[6]
> one string split into many array elements
> IDL> one_string = string(string_array, $
> format = '(' + string(n_elements(string_array)) + 'A)')
>
> IDL> help,one_string & print,one_string
> ONE_STRING STRING = 'one string split into many array
elements'
> one string split into many array elements
Thank you, Norbert!
You gave me the idea that I can use a format that isn't variable at all,
but just larger than I'll ever need:
result = STRING( string_array, FORMAT='(16(16384(16384A)))' )
I ran some benchmarks which showed that the above approach is more than
20 times faster (Pentium II 400) than the more obvious explicit looping
algorithm:
result = ''
FOR i=0, N_ELEMENTS(string_array)-1 DO result = result + string_array[i]
As usual, when we avoid explicit looping, etc. in interpreted code we
get a decent speedup. For greater generality, I made it capable of
handling very long arrays. The new approach allows an array of up to
2^32 elements. It was necessary to nest the repeat counts in order to
get around IDL's maximum of 32767. Note that the only way such a large
array could be used would be if many elements were empty strings.
Otherwise the result would be a string longer than 32767 characters,
IDL's limit for string length.
I think this is a bit kludgey, but its so much faster than looping I'll
live with it!
Thank you everyone who took the time to brainstorm this little puzzle
with me.
-- Tom Kluegel
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