Hi, Cliff,
One problem is that you're using where(), when you want which(). The
former returns the actual elements that match the mask criterion, in
this case the elements of $a that correspond to the places where your
mask "$a(0)==1" is true. This is doubly wrong, because the thing
you're asking where() to index is $a itself, which is treated as
flat. You'll note that the first three values of $a(0) are all 1, so
where() is returning the first three values of $a itself: (1,1,2).
Thus your slice is returning columns 3 and 4 (which you want) from
rows 1, 1, and 2 in order.
You almost certainly want the expression "$a->(3:4, which($a((0))==1)"
instead. (The double parens aren't strictly necessary but are cleaner
-- you want to obliterate the 0 dimension, not just reduce it to size
1...)
On Apr 13, 2009, at 5:05 PM, Cliff Sobchuk wrote:
Hi folks, This is my first real foray in to using PDL for an entire
program. The basis of the program is to use Perl to parse values
from a text file that indicate specifics of
[place1 place2 time measurement1 measurement2]
I am using glue to build up the piddle for each col, row index. To
analyze the data though I need to perform stats and histogram
profiles for each place1,place2 of measurement1, measurement2. I
thought that I could simply slice out the data using nslice and
where. However, I don't get what I expect out when I try it on
sample data. I have gone through the documentation, but have not
found any examples to do what I am trying to do.
My example data is :
perldl> p $a
[
[ 1 1 2 3 4]
[ 1 1 7 8 9]
[ 1 1 12 13 14]
[ 2 1 17 18 19]
[ 2 1 22 23 24]
[ 2 1 27 28 29]
[ 3 1 32 33 34]
[ 3 1 37 38 39]
[ 3 1 42 43 44]
]
To get the data for columns 3 & 4 (the measure columns) I used :
p $a->nslice([3,4],$a->where($a(0)==1))
which provided me with :
[
[ 8 9]
[ 8 9]
[13 14]
]
What I expected to get was column 3 & 4 for the mask defined by :
perldl> p ($a(0)==1)->(3,4)
[
[1]
[1]
[1]
[0]
[0]
[0]
[0]
[0]
[0]
]
Can't call method "nslice" without a package or object reference
I don't know why I get the warning/error - but the correct rows were
selected.
What am I doing wrong and how do I get:
[
[ 3 4]
[ 8 9]
[13 14]
]
Thanks,
Cliff Sobchuk
Core RF Field Support Engineer
Phone: (403) 769 2063 / ESN 758
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