matplotlib-users Mailing List for matplotlib

Hello all,
I believe it is an easy thing to do but I haven't figured out how to convert
between coordinate systems using transData or transAxes. Here is the
simple_plot.py
import numpy
import pylab
x = numpy.arange(0.0, 1.0+0.01, 0.01)
y = numpy.cos(2*2*numpy.pi*x)
pylab.plot(x, y)
Here I want to transform y1 to axis scale between 0 and 1.
Also, I want to transform axis scale, say 0.25, to a corresponding y value
in the data coordinates.
pylab.show()
Currently I am doing it manually scaling things with axis limits, etc. I
believe the neat thing is to use the transforms api. Can somebody explain
me how it is done with transforms? I am using 0.98.1.
Thanks in advance,
Nihat

 
Thank you John:
 
I have exported the excel file in csv format and imported as you showed me. When I try to create a plot with the command: plot(a[isfinite(b)],b[isfinite(b)]), I get an error message: index should be int. When I look at the second column from the csv file I see that the values are imported like '23.5' and not like 23.5 and this causes that error. How can I imported the values from all columns without ''
 
Ionut
 
----- Original Message ----
From: John Hunter <jd...@gm...>
To: sandric ionut <san...@ya...>
Cc: Darren Dale <dsd...@gm...>; Matplotlib <mat...@li...>
Sent: Saturday, June 28, 2008 5:19:42 PM
Subject: Re: [Matplotlib-users] plot xy data with missing values
On Sat, Jun 28, 2008 at 9:16 AM, sandric ionut <san...@ya...> wrote:
> Thank you Darren:
>
> The second example is what I need. I have made some test and it looks OK
> I have my data in excel. How can I read from excel files? Is it a special
> tool?
If you save as csv, you can use matplotlib.mlab.csv2rec to get your
data back as a record array. See
http://matplotlib.sourceforge.net/examples/pylab_examples/loadrec.py
JDH
 

On Sat, Jun 28, 2008 at 9:16 AM, sandric ionut <san...@ya...> wrote:
> Thank you Darren:
>
> The second example is what I need. I have made some test and it looks OK
> I have my data in excel. How can I read from excel files? Is it a special
> tool?
If you save as csv, you can use matplotlib.mlab.csv2rec to get your
data back as a record array. See
http://matplotlib.sourceforge.net/examples/pylab_examples/loadrec.py
JDH

Thank you Darren:
 
The second example is what I need. I have made some test and it looks OK
I have my data in excel. How can I read from excel files? Is it a special tool?
 
Thank you again,
 
Ionut
----- Original Message ----
From: Darren Dale <dsd...@gm...>
To: mat...@li...
Cc: sandric ionut <san...@ya...>
Sent: Saturday, June 28, 2008 3:12:48 PM
Subject: Re: [Matplotlib-users] plot xy data with missing values
Hi Sandric,
On Saturday 28 June 2008 04:31:19 sandric ionut wrote:
> Hello:
> I want to draw a multiple line plot using the data from the bottom of the
> email, but I get a error message: <type 'exceptions.AssertionError'>:
> Dimensions of x and y are incompatible, which is normal, because the number
> of values on x are not equal with the number of values on y. The empty
> spaces from the table are missing values (which were not measured for a
> certain moment in time) and I can't replace them with any other values
It is more robust to use a NaN to represent a missed data point. Then when you 
load your data, your arrays will be the same length. There is already some 
support for plotting data with NaNs in it, but the preferred solution is to 
take a further step and use a masked array to mask your missing values. For 
example, at the ipython -pylab prompt:
time=array([1,2,3,4,5])
f1=array([1,2,NaN,4,5])
f1_m=ma.masked_where(isnan(f1),f1)
plot(f1_m)
That will give you a line with a break in it at the missed observation.
> Is it possible to interpolate the missing values or to the draw the plot as:
> on x the time values and on y the f1,f2,f3, represented as a continuous
> line
If you do not want breaks in your line due to the missed observation, you 
could interpolate the missing values yourself, but if you just want a 
continuous line through whatever data you have, you could use numpy's flexible 
indexing and do:
plot(time[isfinite(f1)], f1[isfinite(f1)])
> The plot should look like the image attached, but with a line crossing
> all the points for f1, f2, f3 
> 
> time f1 f2 f3
> 30 3.39  13.55
> 33   16.94
> 35  6.78 
> 36  10.16 
> 37 10.16 13.55 
> 38 13.55  
> 39 16.94 16.94 
> 40   20.33
> 41 20.33 20.33 
> 42 23.71  
> 44  23.71 
All of my suggestions are based on the assumption that you have recorded 
missing values as NaNs. If you can't reformat your data, or insert NaN's for 
missing values when you load it, I'm not sure how to help.
Darren
 

Hi Sandric,
On Saturday 28 June 2008 04:31:19 sandric ionut wrote:
> Hello:
> I want to draw a multiple line plot using the data from the bottom of the
> email, but I get a error message: <type 'exceptions.AssertionError'>:
> Dimensions of x and y are incompatible, which is normal, because the number
> of values on x are not equal with the number of values on y. The empty
> spaces from the table are missing values (which were not measured for a
> certain moment in time) and I can't replace them with any other values
It is more robust to use a NaN to represent a missed data point. Then when you 
load your data, your arrays will be the same length. There is already some 
support for plotting data with NaNs in it, but the preferred solution is to 
take a further step and use a masked array to mask your missing values. For 
example, at the ipython -pylab prompt:
time=array([1,2,3,4,5])
f1=array([1,2,NaN,4,5])
f1_m=ma.masked_where(isnan(f1),f1)
plot(f1_m)
That will give you a line with a break in it at the missed observation.
> Is it possible to interpolate the missing values or to the draw the plot as:
> on x the time values and on y the f1,f2,f3, represented as a continuous
> line
If you do not want breaks in your line due to the missed observation, you 
could interpolate the missing values yourself, but if you just want a 
continuous line through whatever data you have, you could use numpy's flexible 
indexing and do:
plot(time[isfinite(f1)], f1[isfinite(f1)])
> The plot should look like the image attached, but with a line crossing
> all the points for f1, f2, f3 
> 
> time f1 f2 f3
> 30 3.39  13.55
> 33   16.94
> 35  6.78 
> 36  10.16 
> 37 10.16 13.55 
> 38 13.55  
> 39 16.94 16.94 
> 40   20.33
> 41 20.33 20.33 
> 42 23.71  
> 44  23.71 
All of my suggestions are based on the assumption that you have recorded 
missing values as NaNs. If you can't reformat your data, or insert NaN's for 
missing values when you load it, I'm not sure how to help.
Darren

I kind of figured that was the case, upon looking at the code and 
realizing that the only commonality was in the broad purpose of both 
representations. Otherwise, there's really no commonality in the 
details or implementation. I just wanted to see what the "experts" 
thought before I embarked.
Between this and getting a working SkewT and the meteorological 
community will be all set!
Ryan
Eric Firing wrote:
> Ryan,
> 
> Quiver is not quite the right starting point, although parts of it might 
> work--and actually it could be bent into shape. The problem with 
> attempting a direct transformation of arrows into wind barbs is that the 
> arrows are formed with a fixed number of vertices, so everything is done 
> with nice, regular ndarrays. The natural way to make wind barbs would 
> be with the number of vertices depending on the wind speed. One could 
> probably get around this by using the maximum number of vertices, 
> corresponding to the max wind speed, and then letting some of the barbs 
> be zero-length.
> 
> Another difference might be that wind barbs would best be drawn with 
> lines, not with patches.
> 
> It might be worthwhile to start with the Quiver class and modify it as 
> needed. I certainly would not try to include Windbarb functionality as 
> an option or extension of Quiver. At most, one might be able to pull 
> some common functionality out into a base class for both.
> 
> Something I keep wanting to get to is an ellipse variant of quiver; that 
> would be much closer to the present quiver than a windbarb version would.
> 
> In any case, if you can come up with a good windbarb class, that would 
> be great. I expect Jeff Whitaker would like to add that to basemap, too.
> 
> Eric
> 
> 
> Ryan May wrote:
>> Hi,
>>
>> Has anyone ever tried to modify quiver to change away from plotting 
>> arrows? In my quest to make matplotlib useful the meteorological 
>> community at large, I'm trying to be able to plot what we refer to as 
>> wind barbs. Basically, instead of an arrow whose size indicates the 
>> magnitude of the vector field, a wind barb consists of a line whose 
>> alignment indicates the direction of the vector field (like the arrow) 
>> and has a number of lines or triangles along this shaft to indicate 
>> wind speed. It's a little odd and domain specific, but it's a must 
>> for the meteorologist. We like it because, unlike the arrows, you can 
>> pick off the actual wind speed at a point. See here for an example:
>>
>> http://www.rap.ucar.edu/weather/info/about_windbarb.html
>> http://www.rap.ucar.edu/weather/surface/displaySfc.php?region=abi&endDate=20080627&endTime=-1&duration=0 
>>
>>
>> Has anyone ever tried this (I'm pretty sure I know the answer)? 
>> Failing that, can anyone give me an idea of how difficult it might be 
>> for me to tweak quiver to do this?
>>
>> Thanks,
>>
>> Ryan
>>
> 
-- 
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma

Ryan,
Quiver is not quite the right starting point, although parts of it might 
work--and actually it could be bent into shape. The problem with 
attempting a direct transformation of arrows into wind barbs is that the 
arrows are formed with a fixed number of vertices, so everything is done 
with nice, regular ndarrays. The natural way to make wind barbs would 
be with the number of vertices depending on the wind speed. One could 
probably get around this by using the maximum number of vertices, 
corresponding to the max wind speed, and then letting some of the barbs 
be zero-length.
Another difference might be that wind barbs would best be drawn with 
lines, not with patches.
It might be worthwhile to start with the Quiver class and modify it as 
needed. I certainly would not try to include Windbarb functionality as 
an option or extension of Quiver. At most, one might be able to pull 
some common functionality out into a base class for both.
Something I keep wanting to get to is an ellipse variant of quiver; that 
would be much closer to the present quiver than a windbarb version would.
In any case, if you can come up with a good windbarb class, that would 
be great. I expect Jeff Whitaker would like to add that to basemap, too.
Eric
Ryan May wrote:
> Hi,
> 
> Has anyone ever tried to modify quiver to change away from plotting 
> arrows? In my quest to make matplotlib useful the meteorological 
> community at large, I'm trying to be able to plot what we refer to as 
> wind barbs. Basically, instead of an arrow whose size indicates the 
> magnitude of the vector field, a wind barb consists of a line whose 
> alignment indicates the direction of the vector field (like the arrow) 
> and has a number of lines or triangles along this shaft to indicate wind 
> speed. It's a little odd and domain specific, but it's a must for the 
> meteorologist. We like it because, unlike the arrows, you can pick off 
> the actual wind speed at a point. See here for an example:
> 
> http://www.rap.ucar.edu/weather/info/about_windbarb.html
> http://www.rap.ucar.edu/weather/surface/displaySfc.php?region=abi&endDate=20080627&endTime=-1&duration=0
> 
> Has anyone ever tried this (I'm pretty sure I know the answer)? Failing 
> that, can anyone give me an idea of how difficult it might be for me to 
> tweak quiver to do this?
> 
> Thanks,
> 
> Ryan
>