[Numpy-discussion] arrays and : behaviour

Eelco Hoogendoorn hoogendoorn.eelco at gmail.com
Thu May 1 08:33:52 EDT 2014


You problem isn't with colon indexing, but with the interpretation of the
arguments to plot. multiple calls to plot with scalar arguments do not have
the same result as a single call with array arguments. For this to work as
intended, you would need plt.hold(True), for starters, and maybe there are
other subtleties.


On Thu, May 1, 2014 at 1:31 PM, did did <21did21 at gmx.com> wrote:

> Hello all and sorry for my bad english,
>
> i am a beginner with python and i try to save a lot of data in several
> folders in a 4D matrix
> and then to plot two columns of this 4D matrix.
>
> Bellow, i have the code to fill my 4D matrix, it works very well :
>
> [CODE]matrix4D=[]
> for i in Numbers:
>     readInFolder=folderPrefixe+i+"/"
>     matrix3D=[]
>     for j in listeOfdata:
>         nameOfFile=filePrefixe+i+"-"+j+extensionTXT
>         nameOfFile=readInFolder+nameOfFile
>         matrix2D=np.loadtxt(nameOfFile,delimiter=",",skiprows=1)
>         matrix3D.append(matrix2D)
>     matrix4D.append(matrix3D)
> array4D = np.asarray(matrix4D)[/CODE]
>
> But now, i want to plot the third column as function of the third too
> (just for trying) and i use
> this stupid manner that works well :
>
> [CODE]plt.figure(1)
> temp=plt.plot(array4D[0][0][0][0],array4D[0][0][0][0],'bo')
> temp=plt.plot(array4D[0][0][1][0],array4D[0][0][1][0],'bo')
> temp=plt.plot(array4D[0][0][2][0],array4D[0][0][2][0],'bo')
> temp=plt.plot(array4D[0][0][3][0],array4D[0][0][3][0],'bo')
> plt.show()[/CODE]
>
> Now, i want to use a more smart manner and i use ":" like this
>
> [CODE]plt.figure(1)
> temp=plt.plot(array4D[0][0][0:3][0],array4D[0][0][0:3][0],'bo')
> plt.show()[/CODE]
>
> The result should be the same but i don't got the same results!!!
>
> In attachement you have the two corresponding plots, can you explain to me
> with
> i don't have the same plots ??
>
> thanks for all
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>
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