[Numpy-discussion] Simple question about scatter plot graph

Benjamin Root ben.root at ou.edu
Wed Oct 31 21:24:35 EDT 2012

On Wednesday, October 31, 2012, wrote:

> On Wed, Oct 31, 2012 at 8:59 PM, klo uo <klonuo at gmail.com <javascript:;>>
> wrote:
> > Thanks for your reply
> >
> > I suppose, variable length signals are split on equal parts and dominant
> > harmonic is extracted. Then scatter plot shows this pattern, which has
> some
> > low correlation, but I can't abstract what could be concluded from grid
> > pattern, as I lack statistical knowledge.
> > Maybe it's saying that data is quantized, which can't be easily seen from
> > single sample bar chart, but perhaps scatter plot suggests that? That's
> only
> > my wild guess
> http://pandasplotting.blogspot.ca/2012/06/lag-plot.html
> In general you would see a lag autocorrelation structure in the plot.
> My guess is that even if there is a pattern in your data we might not
> see it because we don't see plots that are plotted on top of each
> other. We only see the support of the y_t, y_{t+1} transition (points
> that are at least once in the sample), but not the frequencies (or
> conditional distribution).
> If that's the case, then
> reduce alpha level so many points on top of each other are darker, or
> colorcode the histogram for each y_t: bincount for each y_t and
> normalize, or use np.histogram directly for each y_t, then assign to
> each point a colorscale depending on it's frequency.
> Did you calculate the correlation? (But maybe linear correlation won't
> show much.)
> Josef

The answer is hexbin() in matplotlib when you have many points laying on or
near each other.

Ben Root
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