| vector of bin indices using histogram? [message #50794] |
Wed, 18 October 2006 05:04 |
greg michael
Messages: 163
Registered: January 2006
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Senior Member |
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Can anyone suggest a good way to get a vector of bin indices using
histogram?
IDL> x=randomu(0,10)
IDL> print,x
0.415999 0.0919649 0.756410 0.529700 0.930436
0.383502 0.653919 0.0668422 0.722660 0.671149
I make a histogram anyway:
IDL> h=histogram(x,binsize=.1)
And I also want to know which bin each element went into:
i.e. b=[4,0,7,5,9,3,6,0,7,6]
I could calculate that from the original data of course, but I'm sure
there must be a trick to get it out of the reverse_indices more
efficiently (when n_elements is huge).
---
While experimenting, I came across this, which is not nice...
IDL> x=randomu(0,100)*1000.
IDL> print,histogram(x,nbins=4)
31 34 34 1
The max value sometimes ends up in a bin of its own (usually this last
bin is zero - I suppose it's a rounding problem).
---
And then a question about reverse_indices - (I think it's not touched
in JD's tutorial):
why are the two parts shoved into a single array? Is there an
application where this arrangement gives some benefit? Wouldn't the
first half make more sense indexing a second separate vector without
the need for this offset?
regards,
Greg
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