Re: [Matplotlib-users] connecting data points...

[Vincent B. <bo...@cl...>]

Hi everybody.

Related to this discussion, here is something else that could be very 
useful for me :

Let's say

t =[0,5,15,18]
s = [1,9,-5]

I'd like to plot a curve f(x) using s and t in a way that :
	- f(x)=1 for x in [0,5]
	- f(x)=9 for x in [5,15]
	- f(x)=-51 for x in [5,18]

Is there already a simple way to do that using Matplotlib, and if not, would it be possible to add it?

Thanx
Vincent



John Hunter wrote:

>>>>>>"Peter" == Peter Groszkowski <pgr...@ge...> writes:
>>>>>>
>
>    Peter> Hi everyone: I was wondering whether it is possible to tell
>    Peter> matplotlib how/when to connect data points. Consider this
>    Peter> simple script:
>
>    Peter> from matplotlib.matlab import * figure(1) t =
>    Peter> [0,1,2,3,4,5,105,106,107] s = [1,4,5,3,9,11,-5,-8,3]
>    Peter> plot(t, s, antialiased=False) grid(True) show()
>
>
>    Peter> There are no data points between t=5 and t=105. By default
>    Peter> the points (5,11) and (105,-5) are connected, but I would
>    Peter> like to tell matplotlib NOT to do so. In my case I would
>    Peter> like to pass the plot function a variable telling it what
>    Peter> to do. So for example would have:
>
>    Peter> plot(t, s, max_delta=40)
>
>    Peter> This would mean that the points are only to be connected if
>    Peter> the difference between the adjacent t values is less than
>    Peter> 40.  In my case this is relevant because sometimes there
>    Peter> are "holes" in my data, and connecting the points makes the
>    Peter> plots look very messy.
>
>    Peter> Would anyone find something like this useful? Would it be
>    Peter> difficult to implement?
>
>Certainly not difficult, and probably useful enough to put in the
>standard distro.  Eg, in a stock market trading example, you would
>have lots of quotes, minute by minute, punctuated by long intervals
>overnight where the market is closed.  If you set maxdelta
>appropriately, you could draw connected lines only within trading
>days.
>
>Here is a sample implementation
>
>from matplotlib.matlab import *
>def segplot(x, y, fmt, maxdelta, **kwargs):
>    """
>    Plot x versus y, breaking the plot at any point where x[i] -
>    x[i-1] > maxdelta. kwargs are passed on to plot
>    """
>    x = asarray(x)
>    y = asarray(y)
>    d = diff(x)
>    lines = []
>    ind = nonzero(greater(d, maxdelta))
>    ind = ind+1
>    if not len(ind):
>        lines.extend( plot(x,y,fmt,**kwargs) ) 
>    else:
>        allind = [0]
>        allind.extend(ind)
>        allind.append(len(x))
>        for i1,i2 in zip(allind[:-1], allind[1:]):
>            lines.extend( plot(x[i1:i2], y[i1:i2], fmt, **kwargs) )
>    return lines
>
>t = [0,1,2,3,4,5,105,106,107,187, 200, 212, 300, 320]
>s = [1,4,5,3,9,11,-5,-8,3,12, 15, 12, -1, 3]
>segplot(t, s, 'b-o', 40, antialiased=False)
>grid(True)
>show()
>
>I'm inclined not to make this part of plot, since plot processes a
>variable number of arguments it makes it a little difficult.
>Certainly doable, but I'm hesitant to put too much on plot because it
>might become unwieldy.  But a new function, like segment plot, would
>be easy enough to include.
>
>Any suggestions for a name, or additional functionality?
>
>JDH
>
>
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