| Re: missing data [message #2237] |
Thu, 16 June 1994 06:58 |
thompson
Messages: 584
Registered: August 1991
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Senior Member |
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caron@acd.ucar.edu (John Caron) writes:
> 3) On bloodsucking support fees:
> $200/year is a pretty low price for service. Any vertical niche company
> like RSI needs to make customer service self supporting. I would like for RSI
> to make avaliable things like known bugs, and other tech documents, that cost
> them little and can save users lots. Also an e-mail address to RSI to report
> possible bugs. Also a language summary on a single page. Also a "see also"
> section for each routine in the reference manual. Also hypertext help. Ok Ill
> stop now.....
One thing that I would like to point out is that one can designate a single
person to act as the contact point with RSI, so that $200/year can cover a
bunch of people. In fact, RSI themselves suggest that you do this. As I
recall, the original post (which I don't have access to anymore) stated that
RSI required you to spend $200/year for each and every person using IDL which
isn't true.
Some of what you want is probably best handled through a World Wide Web
interface. They have one service available now at URL
http://sslab.colorado.edu:2222/projects/IDL/idl_ssl_home.htm l
and I understand that they're working on their own WWW server which will
support the sorts of things you're talking about (or at least I hope it would).
Bill Thompson
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| Re: missing data [message #2240 is a reply to message #2237] |
Wed, 15 June 1994 13:36  |
velt
Messages: 19
Registered: June 1994
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Junior Member |
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In article lp3@ncar.ucar.edu, caron@acd.ucar.edu (John Caron) writes:
> 1) efficiency of where():
>
> Can anyone comment on the efficiency of using:
>
> max = max( my_arr(where(my_arr ne missing_data)))
>
> to find the maximum value of an array, but excluding
> missing values?
It seems fairly trivial, depending on how you code the missing data.
As long is the missing data has a value less than the maximum value
in your array (which is guaranteed if your missing data is less than
all not-missing data), you can remove the where all together. Where
is pretty efficient though.
>
> the array here has size 63000 elements, and only a few (0 - 30)
> are "missing". I am imagining that the where() command returns
> an array of indices, which then is used to grab just those indices
> out of my_arr.
>
> In a higher level language I could make a single pass through my_arr
> to find the max value, excluding the missing data as I go.
I guess you mean a *lower* level language
> Is there a more efficient way to do this in IDL, or is this just
> the price we pay for its generality?
I don't know if any of the following are more efficient (likely not),
but there are more general ways of dealing with the problem. You can
think of the histogram function, or the uniq function. Each of these
will give you (after simple manipulation) a list of values present,
which you can then test against not-allowed values. If you have only
one not-allowed value (such as a missing value), you are best off with
your line.
Robert Velthuizen.
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