I have a very large list of integers representing data needed for a
histogram that I'm going to plot using pylab. However, most of these
values (85%-95%) are zero and I would like to remove them to reduce
the amount of memory I'm using and save time when it comes to plotting
the data. To do this, I'm trying to find the best way to remove all of
the zero values and produce a list of indices of where the non-zero
values used to be.
For example, if my original list is [0,0,1,2,1,0,0] I would like to
produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
of where the non-zero values used to be). Removing non-zero values is
very easy but determining the indicies is where I'm having difficulty.
Thanks in advance for any help
7  6294 
Try this:
>>li=[0,0,1,2,1,0,0]
li
[0, 0, 1, 2, 1, 0, 0]
>>[i for i in range(len(li)) if li[i] != 0]
[2, 3, 4]
Cheers,
Raj
On Tue, Jul 8, 2008 at 10:26 PM, Benjamin Goudey <bw******@gmail .comwrote:
I have a very large list of integers representing data needed for a
histogram that I'm going to plot using pylab. However, most of these
values (85%-95%) are zero and I would like to remove them to reduce
the amount of memory I'm using and save time when it comes to plotting
the data. To do this, I'm trying to find the best way to remove all of
the zero values and produce a list of indices of where the non-zero
values used to be.
For example, if my original list is [0,0,1,2,1,0,0] I would like to
produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
of where the non-zero values used to be). Removing non-zero values is
very easy but determining the indicies is where I'm having difficulty.
Thanks in advance for any help
--
http://mail.python.org/mailman/listinfo/python-list
--
"For him who has conquered the mind, the mind is the best of friends;
but for one who has failed to do so, his very mind will be the
greatest enemy."
Rajanikanth
Benjamin Goudey <bw******@gmail .comwrites:
For example, if my original list is [0,0,1,2,1,0,0] I would like to
produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
of where the non-zero values used to be). Removing non-zero values
is very easy but determining the indicies is where I'm having
difficulty.
The built-in 'enumerate' function is made for this. Creating the new
list can be done efficiently and clearly with a list comprehension.
Further, presumably you want to do further operations on these new
series of data; wouldn't it be better to have the values and original
indices actually correlated together?
This code produces a two-element tuple for each original non-zero
value:
>>sparse_data = [0, 0, 1, 2, 1, 0, 0]
nonzero_dat a = [(index, value)
... for (index, value) in enumerate(spars e_data)
... if value != 0]
>>nonzero_dat a
[(2, 1), (3, 2), (4, 1)]
>>for (index, value) in nonzero_data:
... print "Value %(value)r was originally at index %(index)r" % vars()
...
Value 1 was originally at index 2
Value 2 was originally at index 3
Value 1 was originally at index 4
--
\ “Experience is that marvelous thing that enables you to |
`\ recognize a mistake when you make it again.” —Franklin P. Jones |
_o__) |
Ben Finney
This could work:
l = [0,0,1,2,1,0,0]
indexes, values = zip(*((index,va lue) for index,value in enumerate(l) if value
!= 0))
But I guess it would be a little less cryptic (and maybe a lot more efficient)
if there were an unzip function instead of using the zip(*sequence) trick..
I think a more readable way would be:
indexes = [index for index,value in enumerate(l) if value != 0]
values = [value for value in l if value != 0]
Cheers.
--
Luis Zarrabeitia
Facultad de Matemtica y Computacin, UH http://profesores.matcom.uh.cu/~kyrie
Quoting Benjamin Goudey <bw******@gmail .com>:
I have a very large list of integers representing data needed for a
histogram that I'm going to plot using pylab. However, most of these
values (85%-95%) are zero and I would like to remove them to reduce
the amount of memory I'm using and save time when it comes to plotting
the data. To do this, I'm trying to find the best way to remove all of
the zero values and produce a list of indices of where the non-zero
values used to be.
For example, if my original list is [0,0,1,2,1,0,0] I would like to
produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
of where the non-zero values used to be). Removing non-zero values is
very easy but determining the indicies is where I'm having difficulty.
Thanks in advance for any help
--
http://mail.python.org/mailman/listinfo/python-list
2008/7/9 Benjamin Goudey <bw******@gmail .com>:
I have a very large list of integers representing data needed for a
histogram that I'm going to plot using pylab. However, most of these
values (85%-95%) are zero and I would like to remove them to reduce
the amount of memory I'm using and save time when it comes to plotting
the data. To do this, I'm trying to find the best way to remove all of
the zero values and produce a list of indices of where the non-zero
values used to be.
For example, if my original list is [0,0,1,2,1,0,0] I would like to
produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
of where the non-zero values used to be). Removing non-zero values is
very easy but determining the indicies is where I'm having difficulty.
Thanks in advance for any help
>>l = [0, 0, 1, 2, 1, 0, 0]
zip(*[(item, index) for (index, item) in enumerate(l) if item != 0])
[(1, 2, 1), (2, 3, 4)]
--
http://mail.python.org/mailman/listinfo/python-list
--
Wbr, Andrii Mishkovskyi.
He's got a heart of a little child, and he keeps it in a jar on his desk.
On Jul 9, 7:48*am, "Rajanikant h Jammalamadaka" <rajanika...@gm ail.com>
wrote:
Try this:
>li=[0,0,1,2,1,0,0]
li
[0, 0, 1, 2, 1, 0, 0]>>[i for i in range(len(li)) if li[i] != 0]
[2, 3, 4]
Cheers,
Raj
On Tue, Jul 8, 2008 at 10:26 PM, Benjamin Goudey <bwgou...@gmail .comwrote:
I have a very large list of integers representing data needed for a
histogram that I'm going to plot using pylab. However, most of these
values (85%-95%) are zero and I would like to remove them to reduce
the amount of memory I'm using and save time when it comes to plotting
the data. To do this, I'm trying to find the best way to remove all of
the zero values and produce a list of indices of where the non-zero
values used to be.
For example, if my original list is [0,0,1,2,1,0,0] I would like to
produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
of where the non-zero values used to be). Removing non-zero values is
very easy but determining the indicies is where I'm having difficulty.
Thanks in advance for any help
--
http://mail.python.org/mailman/listinfo/python-list
--
"For him who has conquered the mind, the mind is the best of friends;
but for one who has failed to do so, his very mind will be the
greatest enemy."
Rajanikanth
That's a waste
>>li=[0,0,1,2,1,0,0]
[i for i in li if i]
That's all you need. :)
On Jul 9, 7:48*am, "Rajanikant h Jammalamadaka" <rajanika...@gm ail.com>
wrote:
Try this:
>li=[0,0,1,2,1,0,0]
li
[0, 0, 1, 2, 1, 0, 0]>>[i for i in range(len(li)) if li[i] != 0]
[2, 3, 4]
Cheers,
Raj
On Tue, Jul 8, 2008 at 10:26 PM, Benjamin Goudey <bwgou...@gmail .comwrote:
I have a very large list of integers representing data needed for a
histogram that I'm going to plot using pylab. However, most of these
values (85%-95%) are zero and I would like to remove them to reduce
the amount of memory I'm using and save time when it comes to plotting
the data. To do this, I'm trying to find the best way to remove all of
the zero values and produce a list of indices of where the non-zero
values used to be.
For example, if my original list is [0,0,1,2,1,0,0] I would like to
produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
of where the non-zero values used to be). Removing non-zero values is
very easy but determining the indicies is where I'm having difficulty.
Thanks in advance for any help
--
http://mail.python.org/mailman/listinfo/python-list
--
"For him who has conquered the mind, the mind is the best of friends;
but for one who has failed to do so, his very mind will be the
greatest enemy."
Rajanikanth
Whoops, misread the question
li =[0,0,1,2,1,0,0]
[(index,data) for index,data in enumerate(li) if data]
On Jul 9, 12:26*am, Benjamin Goudey <bwgou...@gmail .comwrote:
I have a very large list of integers representing data needed for a
histogram that I'm going to plot using pylab. However, most of these
values (85%-95%) are zero and I would like to remove them to reduce
the amount of memory I'm using and save time when it comes to plotting
the data. To do this, I'm trying to find the best way to remove all of
the zero values and produce a list of indices of where the non-zero
values used to be.
For example, if my original list is [0,0,1,2,1,0,0] I would like to
produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
of where the non-zero values used to be). Removing non-zero values is
very easy but determining the indicies is where I'm having difficulty.
>>sparse_data = [0, 0, 1, 2, 1, 0, 0]
values,locn s = zip(*[ (x,i) for i,x in enumerate(spars e_data) if x ])
print values
(1, 2, 1)
>>print locns
(2, 3, 4)
>>>
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