Re: Problem with numpy 2D Histogram
Jamie Mitchell wrote:
Hi folks,
I'm trying to plot a 2D histogram but I'm having some issues:
from pylab import *
import numpy as np
import netCDF4
hist,xedges,yedges=np.histogram2d(x,y,bins=10)
extent=[xedges[0],xedges[-1],yedges[0],yedges[-1]]
imshow(hist.T,extent=extent,interpolation='nearest')
colorbar()
show()
After the first line of code I get:
TypeError: Cannot cast array data from dtype('O') to dtype('float64')
according to the rule 'safe'
I'm using python2.7, x and y are type 'numpy.ndarray'
The error message complains about the dtype, i. e. the type of the elements
in the array, not the array itself. Make sure the elements are floating
point numbers or something compatible, not arbitrary Python objects.
As a baseline the following works
from pylab import *
import numpy as np
x, y = np.random.randn(2, 100)
print x, type(x), x.dtype
print y, type(y), y.dtype
hist, xedges, yedges = np.histogram2d(x, y, bins=10)
extent = [xedges[0], xedges[-1], yedges[0], yedges[-1]]
imshow(hist.T, extent=extent, interpolation='nearest')
colorbar()
show()
while this doesn't:
#...
x, y = np.random.randn(2, 100)
import decimal
y = np.array([decimal.Decimal.from_float(v) for v in y])
#...
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Re: Problem with numpy 2D Histogram
On Friday, June 20, 2014 10:25:44 AM UTC+1, Peter Otten wrote:
Jamie Mitchell wrote:
Hi folks,
I'm trying to plot a 2D histogram but I'm having some issues:
from pylab import *
import numpy as np
import netCDF4
hist,xedges,yedges=np.histogram2d(x,y,bins=10)
extent=[xedges[0],xedges[-1],yedges[0],yedges[-1]]
imshow(hist.T,extent=extent,interpolation='nearest')
colorbar()
show()
After the first line of code I get:
TypeError: Cannot cast array data from dtype('O') to dtype('float64')
according to the rule 'safe'
I'm using python2.7, x and y are type 'numpy.ndarray'
The error message complains about the dtype, i. e. the type of the elements
in the array, not the array itself. Make sure the elements are floating
point numbers or something compatible, not arbitrary Python objects.
As a baseline the following works
from pylab import *
import numpy as np
x, y = np.random.randn(2, 100)
print x, type(x), x.dtype
print y, type(y), y.dtype
hist, xedges, yedges = np.histogram2d(x, y, bins=10)
extent = [xedges[0], xedges[-1], yedges[0], yedges[-1]]
imshow(hist.T, extent=extent, interpolation='nearest')
colorbar()
show()
while this doesn't:
#...
x, y = np.random.randn(2, 100)
import decimal
y = np.array([decimal.Decimal.from_float(v) for v in y])
#...
Thanks Peter.
I have changed my x and y data to float64 types but I am still getting the same
error message?
Cheers,
Jamie
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Re: Problem with numpy 2D Histogram
Jamie Mitchell wrote: I have changed my x and y data to float64 types but I am still getting the same error message? Please double-check by adding assert x.dtype == np.float64 assert y.dtype == np.float64 If none of these assertions fail try to make a minimal script including some data that provokes the TypeError and post it here. -- https://mail.python.org/mailman/listinfo/python-list
Re: Problem with numpy 2D Histogram
On Friday, June 20, 2014 12:00:15 PM UTC+1, Peter Otten wrote:
Jamie Mitchell wrote:
I have changed my x and y data to float64 types but I am still getting the
same error message?
Please double-check by adding
assert x.dtype == np.float64
assert y.dtype == np.float64
If none of these assertions fail try to make a minimal script including some
data that provokes the TypeError and post it here.
OK this is my code:
swh_Q0_con_sw=netCDF4.Dataset('/data/cr1/jmitchel/Q0/swh/controlperiod/south_west/swhcontrol_swest_annavg.nc','r')
hs_Q0_con_sw=swh_Q0_con_sw.variables['hs'][:]
x=hs_Q0_con_sw.astype(float64)
# When I print the dtype of x here it says 'float64'
mwp_Q0_con_sw=netCDF4.Dataset('/data/cr1/jmitchel/Q0/mean_wave_period/south_west/controlperiod/mwpcontrol_swest_annavg1D.nc','r')
te_Q0_con_sw=mwp_Q0_con_sw.variables['te'][:]
y=te_Q0_con_sw.astype(float64)
If I try assert x.dtype == np.float64 I get:
AssertionError
hist,xedges,yedges=np.histogram2d(x,y,bins=10)
TypeError: Cannot cast array data from dtype('O') to dtype('float64') according
to the rule 'safe'
Thanks,
Jamie
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Re: Problem with numpy 2D Histogram
Jamie Mitchell wrote:
On Friday, June 20, 2014 12:00:15 PM UTC+1, Peter Otten wrote:
Jamie Mitchell wrote:
I have changed my x and y data to float64 types but I am still getting
the
same error message?
Please double-check by adding
assert x.dtype == np.float64
assert y.dtype == np.float64
If none of these assertions fail try to make a minimal script including
some
data that provokes the TypeError and post it here.
OK this is my code:
swh_Q0_con_sw=netCDF4.Dataset('/data/cr1/jmitchel/Q0/swh/controlperiod/south_west/swhcontrol_swest_annavg.nc','r')
hs_Q0_con_sw=swh_Q0_con_sw.variables['hs'][:]
x=hs_Q0_con_sw.astype(float64)
# When I print the dtype of x here it says 'float64'
mwp_Q0_con_sw=netCDF4.Dataset('/data/cr1/jmitchel/Q0/mean_wave_period/south_west/controlperiod/mwpcontrol_swest_annavg1D.nc','r')
te_Q0_con_sw=mwp_Q0_con_sw.variables['te'][:]
y=te_Q0_con_sw.astype(float64)
If I try assert x.dtype == np.float64 I get:
AssertionError
That means the dtype is not np.float64. As I have neither the data nor the
netCDF4 library to replicate your problem I'm out.
What you might try is to construct a numpy array explicitly
x = np.array([float(v) for v in swh_Q0_con_sw.variables[hs]])
but that's just a stab in the dark.
hist,xedges,yedges=np.histogram2d(x,y,bins=10)
TypeError: Cannot cast array data from dtype('O') to dtype('float64')
according to the rule 'safe'
Thanks,
Jamie
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Re: Problem with numpy 2D Histogram
On Friday, June 20, 2014 9:46:29 AM UTC+1, Jamie Mitchell wrote:
Hi folks,
I'm trying to plot a 2D histogram but I'm having some issues:
from pylab import *
import numpy as np
import netCDF4
hist,xedges,yedges=np.histogram2d(x,y,bins=10)
extent=[xedges[0],xedges[-1],yedges[0],yedges[-1]]
imshow(hist.T,extent=extent,interpolation='nearest')
colorbar()
show()
After the first line of code I get:
TypeError: Cannot cast array data from dtype('O') to dtype('float64')
according to the rule 'safe'
I'm using python2.7, x and y are type 'numpy.ndarray'
Cheers,
Jamie
Thanks for your help Peter.
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