| Re: Unpacking algorithm [message #39317] |
Mon, 17 May 2004 06:41 |
Timm Weitkamp
Messages: 66
Registered: August 2002
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Member |
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Tmorri:
If I have understood your problem, then the following might do the job
(given your vector v0, of which you want to get every 4th element into
v1 and the others into v2).
i0 = INDGEN(N_ELEMENTS(v0))
i1 = WHERE((i0 MOD 4) EQ 0, COMPLEMENT=i2)
v1 = v0[i1]
v2 = v0[i2]
Hope this helps,
Timm
PS. I'm sure there's a better way than using WHERE, but I don't like to
think.
On 15.05.04 at 19:00 -0400, Tmorri wrote:
> one second thought,
>
> Does any one have an algorithm to unpack this vector
>
>
> v0=[0 x1 x2 x3 0 x4 x5 x1 0 x2 x3 x4 0 x5 x1 x2 0 x3 x4 x5]
>
> in the following way:
>
> v1=[0 0 0 0 0]
>
> v2=[x1 x2 x3 x4 x5 x1 x2 x3 x4 x5 x1 x2 x3 x4 x5]
>
> x1,x2,x3,x4,x5 are variables that can take any value, even zero, (0).
>
> I just want to get rid othe zeroes (every fourth element)shown in vector
> v0
>
>
> Thanks,
>
> Tmorri
>
>
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| Re: Unpacking algorithm [message #39322 is a reply to message #39317] |
Sun, 16 May 2004 21:37  |
MKatz843
Messages: 98
Registered: March 2002
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Member |
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You could also use where() to find the indices of the "zero" elements,
or their complement, that is the indices of the non-zero elements.
v0=[0 x1 x2 x3 0 x4 x5 x1 0 x2 x3 x4 0 x5 x1 x2 0 x3 x4 x5]
w2 = where(v0 NE 0, complement=w1) ;--- returns an array of indices
v2 = v0(w2)
v1 = v0(w1)
There are also very handy keywords: count and ncomplement that return
the number of indices of each kind that are found. Note that where()
returns -1 when there are no matches. If you try to use v0(w1) and w1
is -1 you'll get an error. That's where the count variables come in. I
usually do something like "if count GT 0 then (do something)" to avoid
the error.
M. Katz
"Tmorri" <torrimorri@yahoo.com> wrote in message news:<52e0072063f360e0705e8ac96f274e52@localhost.talkaboutprogramming.com>...
> one second thought,
>
> Does any one have an algorithm to unpack this vector
>
>
> v0=[0 x1 x2 x3 0 x4 x5 x1 0 x2 x3 x4 0 x5 x1 x2 0 x3 x4 x5]
>
> in the following way:
>
> v1=[0 0 0 0 0]
>
> v2=[x1 x2 x3 x4 x5 x1 x2 x3 x4 x5 x1 x2 x3 x4 x5]
>
> x1,x2,x3,x4,x5 are variables that can take any value, even zero, (0).
>
> I just want to get rid othe zeroes (every fourth element)shown in vector
> v0
>
>
> Thanks,
>
> Tmorri
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| Re: Unpacking algorithm [message #39324 is a reply to message #39322] |
Sun, 16 May 2004 08:19 |
Christopher Lee
Messages: 4
Registered: February 2001
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Junior Member |
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> v0=[0 x1 x2 x3 0 x4 x5 x1 0 x2 x3 x4 0 x5 x1 x2 0 x3 x4 x5]
>
> I just want to get rid othe zeroes (every fourth element)shown in vector
> v0
n=n_elements(v0)
s=4
index=(findgen(s,fix((n+3)/s)))[1:s-1,*]
index=reform(index, n_elements(index))
;index skips all of the mod 4 indices
new_v=v0[index]
;or even shorter, if n_elements(v0) mod s = 0
s=4
v0=reform((reform(v0,s,n_elements(v0)/s))[1:s-1,*],n_element s(v0)*(s-1)/s)
Chris.
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| Re: Unpacking algorithm [message #39327 is a reply to message #39324] |
Sat, 15 May 2004 16:00 |
Tmorri
Messages: 10
Registered: April 2004
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Junior Member |
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one second thought,
Does any one have an algorithm to unpack this vector
v0=[0 x1 x2 x3 0 x4 x5 x1 0 x2 x3 x4 0 x5 x1 x2 0 x3 x4 x5]
in the following way:
v1=[0 0 0 0 0]
v2=[x1 x2 x3 x4 x5 x1 x2 x3 x4 x5 x1 x2 x3 x4 x5]
x1,x2,x3,x4,x5 are variables that can take any value, even zero, (0).
I just want to get rid othe zeroes (every fourth element)shown in vector
v0
Thanks,
Tmorri
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