| Re: manipulating structures [message #53358 is a reply to message #53357] |
Sun, 08 April 2007 07:06   |
Kenneth P. Bowman
Messages: 585
Registered: May 2000
|
Senior Member |
|
|
In article <1175997980.025055.256650@e65g2000hsc.googlegroups.com>,
"metachronist" <rkombiyil@gmail.com> wrote:
> Thanks much! I don't trust myself in such circumstances and hence I
> agree with Dr.B :-) This prompts me to ask another trivial question,
> if I may..Since I have lots of missing data, and I do lots of math
> operations (array ops, fft etc. etc.), will these (NaN) propagate all
> the way through in such situations? Should I be using them in
> conjunction with finite statement? Any pointers as to where one oughta
> be careful with these NaNs?
>
> Thanks in advance for your time and sharing your experience,
> ~rk
Many IDL functions include /NAN keywords to skip NaNs in operations
(TOTAL, MEAN, etc.). In other cases, you will have to find the good
data with WHERE(FINITE(...), COUNT = count).
There is one special case that you have to watch out for when using
TOTAL with the /NAN keyword. If *all* of the elements are NaNs, the
result returned is not a NaN, but a zero.
IDL> x = replicate(!values.f_nan, 5)
IDL> print, x
NaN NaN NaN NaN NaN
IDL> print, total(x)
NaN
IDL> print, total(x, /nan)
0.00000
I think this is a serious implementation bug because it renders the
/NAN keyword useless in most circumstances, but I guess we are stuck
with it.
Inconsistently, this happens with TOTAL, but not with MEAN
IDL> print, mean(x, /nan)
NaN
Ken
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
