# There is an index error occuring when iam trying to estimate rain rate using python wradlib

**URL:** <https://openradar.discourse.group/t/there-is-an-index-error-occuring-when-iam-trying-to-estimate-rain-rate-using-python-wradlib/400>\
**Category:** Openradar\
**Tags:** wradlib\
**Created:** [February 15, 2024, 8:04am UTC](https://openradar.discourse.group/t/there-is-an-index-error-occuring-when-iam-trying-to-estimate-rain-rate-using-python-wradlib/400 "2024-02-15T08:04:56Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![ankithva](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/ankithva/32/317_2.png) [@ankithva](https://openradar.discourse.group/u/ankithva)\
**Post date:** [February 15, 2024, 8:04am UTC](https://openradar.discourse.group/t/there-is-an-index-error-occuring-when-iam-trying-to-estimate-rain-rate-using-python-wradlib/400/1 "2024-02-15T08:04:56Z")

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grid2 = pyart.io.read\_grid(“D:/radar data/radinout/griddedradout20/griddedradout20grid\_ZDR\_JPR220620165253-IMD-B.nc”)

xg2 = grid2.to\_xarray()  
Z1 = wrl.trafo.idecibel(xg1.REF[0,0])  
rain1 = wrl.zr.z\_to\_r(Z1,a = 200,b=1.6)#marshal palmer

There is an index error occuring when iam trying to estimate rain rate using python :

* * *

IndexError Traceback (most recent call last)  
Cell In[95], line 1  
----\> 1 rain1 = wrl.zr.z\_to\_r(Z1,a = 200,b=1.6)#marshal palmer

File ~\PYTHON\envs\pcf\lib\functools.py:888, in singledispatch..wrapper(\*args, \*\*kw)  
884 if not args:  
885 raise TypeError(f’{funcname} requires at least ’  
886 ‘1 positional argument’)  
 → 888 return dispatch(args[0]. **class** )(\*args, \*\*kw)

File ~\PYTHON\envs\pcf\lib\site-packages\wradlib\zr.py:96, in \_z\_to\_r\_xarray(obj, \*\*kwargs)  
65 @z\_to\_r.register(xr.DataArray)  
66 def \_z\_to\_r\_xarray(obj, \*\*kwargs):  
67 “”“Conversion from reflectivities to rain rates.  
68  
69 Calculates rain rates from radar reflectivities using  
(…)  
94 rainfall intensity in mm/h  
95 “””  
—\> 96 dim0 = obj.wrl.util.dim0()  
97 out = xr.apply\_ufunc(  
98 z\_to\_r,  
99 obj,  
(…)  
104 dask\_gufunc\_kwargs=dict(allow\_rechunk=True),  
105 )  
106 out.attrs = sweep\_vars\_mapping[“RATE”]

File ~\PYTHON\envs\pcf\lib\site-packages\wradlib\util.py:1504, in UtilMethods.dim0(self, \*args, \*\*kwargs)  
1502 return dim0(self, \*args, \*\*kwargs)  
1503 else:  
 → 1504 return dim0(self.\_obj, \*args, \*\*kwargs)

File ~\PYTHON\envs\pcf\lib\site-packages\wradlib\util.py:1410, in dim0(obj)  
1408 def dim0(obj):  
1409 “”“Return major dimension (azimuth/elevation) of xarray object.”“”  
 → 1410 return list(set(obj.dims) & {“azimuth”, “elevation”})[-1]

IndexError: list index out of range

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**Author:** ![kmuehlbauer](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/kmuehlbauer/32/439_2.png) [@kmuehlbauer](https://openradar.discourse.group/u/kmuehlbauer)\
**Post date:** [February 15, 2024, 4:18pm UTC](https://openradar.discourse.group/t/there-is-an-index-error-occuring-when-iam-trying-to-estimate-rain-rate-using-python-wradlib/400/2 "2024-02-15T16:18:32Z")

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Hi @ankithva ,

Please show the content of `Z1`. It looks like the dimensions do not have the correct name

Best,  
Kai

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<div class="post-metadata">

**Author:** ![kmuehlbauer](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/kmuehlbauer/32/439_2.png) [@kmuehlbauer](https://openradar.discourse.group/u/kmuehlbauer)\
**Post date:** [February 15, 2024, 4:32pm UTC](https://openradar.discourse.group/t/there-is-an-index-error-occuring-when-iam-trying-to-estimate-rain-rate-using-python-wradlib/400/3 "2024-02-15T16:32:28Z")

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Just realising you are extracting one value from the DataArray. Then just use `Z1.values` in the call to `wrl.zr.z_to_r`.

HTH,  
Kai