# Weird error using az.waic
**URL:** https://discourse.pymc.io/t/weird-error-using-az-waic/10141
**Category:** v5
**Tags:** modeling
**Created:** [August 12, 2022, 10:13pm UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141 "2022-08-12T22:13:02Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@HuangHam](https://discourse.pymc.io/u/HuangHam)
#### Post date: [August 12, 2022, 10:13pm UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141/1 "2022-08-12T22:13:02Z")
When i’m trying to calculate the waic of my trace file, i get the weird error below. Visually inspecting the trace file doesn’t give away any potential error. The likelihood matrix looks reasonable. What could be the cause of this? Would I need to refit the model?
```auto
~/opt/anaconda3/envs/modeling/lib/python3.9/site-packages/arviz/stats/stats.py in waic(data, pointwise, var_name, scale, dask_kwargs)
1668 warn_mg = True
1669
-> 1670 waic_i = scale_value * (lppd_i - vars_lpd)
1671 waic_se = (n_data_points * np.var(waic_i.values)) ** 0.5
1672 waic_sum = np.sum(waic_i.values)
~/opt/anaconda3/envs/modeling/lib/python3.9/site-packages/xarray/core/_typed_ops.py in __sub__ (self, other)
207
208 def __sub__ (self, other):
--> 209 return self._binary_op(other, operator.sub)
210
211 def __mul__ (self, other):
~/opt/anaconda3/envs/modeling/lib/python3.9/site-packages/xarray/core/dataarray.py in _binary_op(self, other, f, reflexive)
3523 if isinstance(other, DataArray):
3524 align_type = OPTIONS["arithmetic_join"]
-> 3525 self, other = align(self, other, join=align_type, copy=False) # type: ignore
...
--> 246 coord_dtype = self.coord_dtype
247 return type(self)(index, dim, coord_dtype)
248
AttributeError: coord_dtype
```
---
### Author:  [@aloctavodia](https://discourse.pymc.io/u/aloctavodia)
#### Post date: [August 13, 2022, 10:36am UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141/2 "2022-08-13T10:36:58Z")
That’s weird. It seems your trace/InferenceData has some weird type. Can you share the trace/InferenceData?
Also I recommend using loo instead of waic.
---
### Author:  [@HuangHam](https://discourse.pymc.io/u/HuangHam)
#### Post date: [August 13, 2022, 1:29pm UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141/3 "2022-08-13T13:29:51Z")
The trace file is too large (2.3G) to be able to upload. When I refit it using a subset of the data I didn’t replicate this issue. Maybe when I uploaded the file to box drive changed the file somehow and corrupted types in it? Because I remember everything was working when I first fitted my models. But after a few days until yesterday when I try to run waic again I get this wierd type error. Why is loo recommended over waic?
---
### Author:  [@aloctavodia](https://discourse.pymc.io/u/aloctavodia)
#### Post date: [August 13, 2022, 1:44pm UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141/4 "2022-08-13T13:44:51Z")
@OriolAbril has you seen something like this?
While theoretically both waic and loo converge, for finite samples loo has been show to provide most robust results than waic, additionally loo offers diagnostics indicating when loo may be failing, something that waic can’t provide.
---
### Author:  [@HuangHam](https://discourse.pymc.io/u/HuangHam)
#### Post date: [August 13, 2022, 1:48pm UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141/5 "2022-08-13T13:48:01Z")
Ah icic. But one of my models has loo value of NaN somehow. Since I’m fitting an RL model on pymc, maybe its complexity or the potential existence of goofy data may cause loo to fail?
Also I saved my trace using:
```auto
with open('real_traces_' + agent.name + '.p', 'wb') as f:
pickle.dump(tr, f)
```
Maybe pickled .p file is not stable somehow?
---
### Author:  [@aloctavodia](https://discourse.pymc.io/u/aloctavodia)
#### Post date: [August 13, 2022, 2:01pm UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141/6 "2022-08-13T14:01:44Z")
You can use [arviz.to\_netcdf — ArviZ dev documentation](https://arviz-devs.github.io/arviz/api/generated/arviz.to_netcdf.html#arviz.to_netcdf) to save data
---
### Author:  [@OriolAbril](https://discourse.pymc.io/u/OriolAbril)
#### Post date: [August 13, 2022, 2:22pm UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141/7 "2022-08-13T14:22:06Z")
From the error it looks like an issue with the dtypes of the data, or probably not even of the data but the coordinates that index the data. Can you share what you get when you run
```auto
print(tr.log_likelihood)
```
for the case that fails? That should include the shapes and dtypes of the different elements and even if not the whole trace to reproduce the error it might already be enough.
I am not expert on pickle, but it is always a source of headaches, I strongly recommend you use `to_netcdf` or `to_zarr`: [InferenceData — ArviZ dev documentation](https://python.arviz.org/en/latest/api/inference_data.html#io-conversion)
---
### Author:  [@HuangHam](https://discourse.pymc.io/u/HuangHam)
#### Post date: [August 13, 2022, 3:06pm UTC](https://discourse.pymc.io/t/weird-error-using-az-waic/10141/8 "2022-08-13T15:06:54Z")
OMG pickle sucks. I loaded the traces files and save them again with to\_netcdf, and load the .nc files. Now it works without error! Thank you both so much for helping me out. I guess the lesson is: don’t use pickle haha