Thanks, Justin
I think I made a confusing example code. Here comes new one:
segs = []
for i in range(0, len(vec)):
x1 = vec[i][0]
#x1 = 3000000
x2 = vec[i][1]
#x2 = 4000000
y1 = y2 = vec[i][2]
segs.extend( [[(x1,y1),(x2,y2)]] )
line_segments = LineCollection(segs, linewidth=3, alpha=0.3, colors =
'r', linestyle = 'solid') ax.add_collection(line_segments)
The above code doesn't show any lines. But if I comment out one or both of
commented parts, the lines are shown.
I mean the below cases are all work.
x1 = vec[i][0]
x2 = 4000000
y1 = y2 = vec[i][2]
or
x1 = 3000000
x2 = vec[i][1]
y1 = y2 = vec[i][2]
I think it's wierd. I'm pretty sure that the 2D array has valid values.
Jin
---
> Date: Wed, 13 Jul 2011 15:32:33 -0400
> Subject: Re: [Matplotlib-users] Question on LineCollection
> From: jne...@gmail.com
> To: sulsj0...@hotmail.com
> CC: matplotlib-users@lists.sourceforge.net
>
> 2011/7/13 SULSEUNG-JIN <sulsj0...@hotmail.com>:
> > Hi,
> >
> > I'm plotting thousands of short lines on a plot. Because "plot" and "Line2D"
> > are quite slow for this case, I'm trying to use lineCollection. Here comes
> > the part of my testing code:
> >
> > ...
> > segs = []
> >
> > # Manual set for testing
> > x2 = np.zeros(2,dtype=int)
> > ys2 = [np.zeros(2,dtype=float)]
> > x2[0] = 1000000
> > x2[1] = 2000000
> > ys2[0][0] = ys2[0][1] = 50
> > segs.extend( [zip(x2,y) for y in ys2] )
> >
> > for i in range(0, len(records)):
> > ...
> > # get xStart, xEnd, and y
> > ...
> >
> > x2[0] = xStart
> > x2[1] = xEnd
> > ys2[0][0] = ys2[0][1] = y
> > segs.extend( [zip(x2,y) for y in ys2] )
> >
> > line_segments = LineCollection(segs, linewidth=4, alpha=0.3, colors =
> > 'r', linestyle = 'solid')
> > ax.add_collection(line_segments)
> > ...
> >
> > The problem I have is only the first segment of the lines in the "segs"
> > which I manually set the values is shown in the plot. If I move the first
> > part in the for loop to test, it works. What am I missing?
> >
> > Thank you in advance.
>
> Are you sure it's the first segment that shows up, and not the last one?
>
> You're reusing the numpy array x2 and the list ys2. You're overwriting
> the values inside them each time through the for loop, but segs just
> contains len(records) references to the exact same arrays in memory
> (x2 and ys2).
>
> The reason it works if you move the first part inside is that it
> creates a new numpy.array x2 and a new python list ys2 each time then,
> which is what you want.
>
> Justin
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