kdeplot raising LinAlgError("singular matrix") instead of warning

[Proch92]

Example code:

import pandas as pd
import seaborn as sns

df = pd.DataFrame({'a': [1929245168.06679]*18})
sns.kdeplot(data=df, x='a')

seaborn version 0.11.2
python version 3.8.12

Error: numpy.linalg.LinAlgError: singular matrix

Expected: UserWarning: Dataset has 0 variance; skipping density estimate. Pass 'warn_singular=False' to disable this warning.

I tried other types of singular matrixes and the singular warning implemented in 0.11.2 work as expected. (for example: pd.DataFrame({'a': [0]*10}) or pd.DataFrame({'a': [0]}))
The problem seem to arise for particular floats. I tried other big floats and changed the value slightly resulting in different outcome.

Another interesting sequence:
pd.DataFrame({'a': [1929245168.06679]*18}) -> error
pd.DataFrame({'a': [1929245160.06679]*18}) -> error
pd.DataFrame({'a': [1929245100.06679]*18}) -> no error and no warning (singular_warn is True)

[mwaskom]

Here is what seaborn is doing

import math
print(observation_variance := df["a"].var(ddof=1))
print(math.isclose(observation_variance, 0) )

5.48132967586363e-13
False

[mwaskom]

I don’t recall if there’s a reason this does a proactive check rather than catching the error, but that may be easier.

[markusschlenker]

Here is what seaborn is doing

import math
print(observation_variance := df["a"].var(ddof=1))
print(math.isclose(observation_variance, 0) )

5.48132967586363e-13
False

Hi,
I didn't know where to best put this question, so please let me know if it is misplaced here. Sorry if this has been discussed elsewhere already.

I was wondering if like it is defined here, math.isclose(observation_variance, 0) will give False even for very small observation_variance because it uses relative tolerance by default. The documentation suggests using abs_tol for comparisons near zero https://docs.python.org/3/library/math.html#math.isclose. Was this considered? On the other hand I guess deciding on an abs_tol value is not a straight forward choice either.

I stumbled upon this for the following example:
sns.pairplot(pd.DataFrame([0] * 7), diag_kind="kde", diag_kws=dict(warn_singular=True)) --> no error, but warning
sns.pairplot(pd.DataFrame([0.34] * 7), diag_kind="kde", diag_kws=dict(warn_singular=True)) --> error, no warning
sns.pairplot(pd.DataFrame([0.341] * 7), diag_kind="kde", diag_kws=dict(warn_singular=True)) --> no error, no warning

I am using
Python 3.7.13
seaborn 0.11.2