transData.transform on 'log' plot

Community matplotlib-users
1

Hello,

When I try to use transData.transform on a log plot, an error occurs :
...
File "E:\Python26\lib\site-packages\matplotlib\transforms.py", line 1895, in transform
     self._a.transform(points))
   File "E:\Python26\lib\site-packages\matplotlib\transforms.py", line 1723, in transform
     x_points = x.transform(points[:, 0])
TypeError: tuple indices must be integers, not tuple

Here is an example :
#!/usr/bin/env python

import matplotlib
matplotlib.use('WXAgg')
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as FigureCanvas
from matplotlib.figure import Figure

import wx

class CanvasFrame(wx.Frame):

     def __init__(self):
         wx.Frame.__init__(self,None,-1,
                          'CanvasFrame',size=(550,350))

         self.SetBackgroundColour(wx.NamedColor("WHITE"))

         self.figure = Figure()

         self.axes = self.figure.add_subplot(111)
         self.axes.set_xscale('log')

         p1 = (1,1)
         p2 = (2,2)
         _x1, _y1 = self.axes.transData.transform(p1)
         _x2, _y2 = self.axes.transData.transform(p2)
         _xy = [[_x1, _y1], [_x2, _y2]]

         xy = self.axes.transData.inverted().transform(_xy)

         self.axes.plot(xy)
         self.canvas = FigureCanvas(self, -1, self.figure)

         self.sizer = wx.BoxSizer(wx.VERTICAL)
         self.sizer.Add(self.canvas, 1, wx.LEFT | wx.TOP | wx.GROW)
         self.SetSizer(self.sizer)
         self.Fit()

class App(wx.App):

     def OnInit(self):
         frame = CanvasFrame()
         frame.Show(True)

         return True

app = App(0)
app.MainLoop()

If I comment the line : self.axes.set_xscale('log'), it works fine.

python 2.6.4
wxpython 2.8.10
mpl 0.99

Thanks by advance for your help.
Cédrick

2

The `transform` method requires that its argument is a numpy array. You "got lucky" with duck typing in the non-log case, but there is an assumption in the transformation code that it can use Numpy array functionality on whatever is passed in. Unfortunately, the transforms code is so low-level and core to matplotlib that any checking or coercing of the types passed in makes a significant impact on interactive performance, so I'm reluctant to add that. The docstring does say this:

        """
        Performs the transformation on the given array of values.

        Accepts a numpy array of shape (N x :attr:`input_dims`) and
        returns a numpy array of shape (N x :attr:`output_dims`).
        """

I've attached a fixed version of your script that uses Numpy arrays rather than tuples for the points.

Mike

C�drick FAURY wrote:

log_transform.py (1.19 KB)

···

Hello,

When I try to use transData.transform on a log plot, an error occurs :
...
File "E:\Python26\lib\site-packages\matplotlib\transforms.py", line 1895, in transform
     self._a.transform(points))
   File "E:\Python26\lib\site-packages\matplotlib\transforms.py", line 1723, in transform
     x_points = x.transform(points[:, 0])
TypeError: tuple indices must be integers, not tuple

Here is an example :
#!/usr/bin/env python

import matplotlib
matplotlib.use('WXAgg')
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as FigureCanvas
from matplotlib.figure import Figure

import wx

class CanvasFrame(wx.Frame):

     def __init__(self):
         wx.Frame.__init__(self,None,-1,
                          'CanvasFrame',size=(550,350))

         self.SetBackgroundColour(wx.NamedColor("WHITE"))

         self.figure = Figure()

         self.axes = self.figure.add_subplot(111)
         self.axes.set_xscale('log')

         p1 = (1,1)
         p2 = (2,2)
         _x1, _y1 = self.axes.transData.transform(p1)
         _x2, _y2 = self.axes.transData.transform(p2)
         _xy = [[_x1, _y1], [_x2, _y2]]

         xy = self.axes.transData.inverted().transform(_xy)

         self.axes.plot(xy)
         self.canvas = FigureCanvas(self, -1, self.figure)

         self.sizer = wx.BoxSizer(wx.VERTICAL)
         self.sizer.Add(self.canvas, 1, wx.LEFT | wx.TOP | wx.GROW)
         self.SetSizer(self.sizer)
         self.Fit()

class App(wx.App):

     def OnInit(self):
         frame = CanvasFrame()
         frame.Show(True)

         return True

app = App(0)
app.MainLoop()

If I comment the line : self.axes.set_xscale('log'), it works fine.

python 2.6.4
wxpython 2.8.10
mpl 0.99

Thanks by advance for your help.
C�drick

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