For my assignment I'm supposed to plot the tracks of 20 hurricanes on a map using matplotlib. However when I run my code I get the error: AssertionError:Grouper and axis must be the same length
Here's the code I have:
import numpy as np
from mpl_toolkits.basemap import Basemap
import matplotlib.pyplot as plt
from PIL import *
fig = plt.figure(figsize=(12,12))
ax = fig.add_axes([0.1,0.1,0.8,0.8])
m = Basemap(llcrnrlon=-100.,llcrnrlat=0.,urcrnrlon=-20.,urcrnrlat=57.,
projection='lcc',lat_1=20.,lat_2=40.,lon_0=-60.,
resolution ='l',area_thresh=1000.)
m.bluemarble()
m.drawcoastlines(linewidth=0.5)
m.drawcountries(linewidth=0.5)
m.drawstates(linewidth=0.5)
# Creates parallels and meridians
m.drawparallels(np.arange(10.,35.,5.),labels=[1,0,0,1])
m.drawmeridians(np.arange(-120.,-80.,5.),labels=[1,0,0,1])
m.drawmapboundary(fill_color='aqua')
# Opens data file
import pandas as pd
name = [ ]
df = pd.read_csv('louisianastormb.csv')
for name, group in df.groupby([name]):
latitude = group.lat.values
longitude = group.lon.values
x,y = m(longitude, latitude)
plt.plot(x,y,'y-',linewidth=2 )
plt.xlabel('Longitude')
plt.ylabel('Latitude')
plt.title('20 Hurricanes with Landfall in Louisiana')
plt.savefig('20hurpaths.jpg', dpi=100)
Here's the full error output:
Traceback (most recent call last):
File "/home/darealmzd/lstorms.py", line 31, in <module>
for name, group in df.groupby([name]):
File "/usr/local/lib/python2.7/dist-packages/pandas/core/generic.py", line 186, in groupby
squeeze=squeeze)
File "/usr/local/lib/python2.7/dist-packages/pandas/core/groupby.py", line 533, in groupby
return klass(obj, by, **kwds)
File "/usr/local/lib/python2.7/dist-packages/pandas/core/groupby.py", line 197, in __init__
level=level, sort=sort)
File "/usr/local/lib/python2.7/dist-packages/pandas/core/groupby.py", line 1325, in _get_grouper
ping = Grouping(group_axis, gpr, name=name, level=level, sort=sort)
File "/usr/local/lib/python2.7/dist-packages/pandas/core/groupby.py", line 1129, in __init__
self.grouper = _convert_grouper(index, grouper)
File "/usr/local/lib/python2.7/dist-packages/pandas/core/groupby.py", line 1350, in _convert_grouper
raise Assertionerror('Grouper and axis must be same length')
Assertionerror: Grouper and axis must be same length
The problem is that you're grouping by (effectively) a list of empty list ([[]]
). Because you have name = []
earlier and then you wrap that in a list as well.
If you want to group on a single column (called 'HurricaneName'), you should do something like:
for name, group in df.groupby('HurricaneName'):
However, if you want to group on multiple columns, then you need to pass a list:
for name, group in df.groupby(['HurricaneName', 'Year'])
If you want to put it in a variable like you have, you can do it like this:
col_name = 'State'
for name, group in df.groupby([col_name]):