Feature analysis using histograms -- LinAlgError: singular matrix

Question

I am trying to create histograms for feature analysis to see how similar high grade tumor and low grade tumor characteristics are. Something similar to the histogram shown below:

Matrix "Z" looks like this and contains 106 features

Matrix "Z"

The code I am using is:

#Import data
data = pd.read_csv("/Users/MLuser/Desktop/Data table - CM_Transposed.csv")

# Prproccess data
bins = (0,2,4)
group_names = ['low_grade','high_grade']
data['FGrade'] = pd.cut(data['FGrade'], bins=bins, labels=group_names)

label_grade = LabelEncoder()
data['FGrade'] = label_grade.fit_transform(data['FGrade'])
Z=data

# Separate the dataset as response variable and feature variables
Z = Z.drop('Feature Name', axis = 1)
Z.columns

low_grade=Z[Z.FGrade==0] # define malignant
high_grade=Z[Z.FGrade==1] # define benign

for i, col in enumerate(Z.columns):
    plt.figure(i)
    sns.distplot(low_grade.iloc[:,i], color='red')
    sns.distplot(high_grade.iloc[:,i], color='g')

Unfortunately when I run the above, I get a single graph and the following error:

---------------------------------------------------------------------------
LinAlgError                               Traceback (most recent call last)
<ipython-input-25-79d6e8cd51a8> in <module>
     27 for i, col in enumerate(Z.columns):
     28     plt.figure(i)
---> 29     sns.distplot(low_grade.iloc[:,i], color='red')
     30     sns.distplot(high_grade.iloc[:,i], color='g')
     31 

~/env/lib/python3.6/site-packages/seaborn/distributions.py in distplot(a, bins, hist, kde, rug, fit, hist_kws, kde_kws, rug_kws, fit_kws, color, vertical, norm_hist, axlabel, label, ax)
    229     if kde:
    230         kde_color = kde_kws.pop("color", color)
--> 231         kdeplot(a, vertical=vertical, ax=ax, color=kde_color, **kde_kws)
    232         if kde_color != color:
    233             kde_kws["color"] = kde_color

~/env/lib/python3.6/site-packages/seaborn/distributions.py in kdeplot(data, data2, shade, vertical, kernel, bw, gridsize, cut, clip, legend, cumulative, shade_lowest, cbar, cbar_ax, cbar_kws, ax, **kwargs)
    689         ax = _univariate_kdeplot(data, shade, vertical, kernel, bw,
    690                                  gridsize, cut, clip, legend, ax,
--> 691                                  cumulative=cumulative, **kwargs)
    692 
    693     return ax

~/env/lib/python3.6/site-packages/seaborn/distributions.py in _univariate_kdeplot(data, shade, vertical, kernel, bw, gridsize, cut, clip, legend, ax, cumulative, **kwargs)
    292                               "only implemented in statsmodels."
    293                               "Please install statsmodels.")
--> 294         x, y = _scipy_univariate_kde(data, bw, gridsize, cut, clip)
    295 
    296     # Make sure the density is nonnegative

~/env/lib/python3.6/site-packages/seaborn/distributions.py in _scipy_univariate_kde(data, bw, gridsize, cut, clip)
    364     """Compute a univariate kernel density estimate using scipy."""
    365     try:
--> 366         kde = stats.gaussian_kde(data, bw_method=bw)
    367     except TypeError:
    368         kde = stats.gaussian_kde(data)

~/env/lib/python3.6/site-packages/scipy/stats/kde.py in __init__(self, dataset, bw_method, weights)
    206             self._neff = 1/sum(self._weights**2)
    207 
--> 208         self.set_bandwidth(bw_method=bw_method)
    209 
    210     def evaluate(self, points):

~/env/lib/python3.6/site-packages/scipy/stats/kde.py in set_bandwidth(self, bw_method)
    552             raise ValueError(msg)
    553 
--> 554         self._compute_covariance()
    555 
    556     def _compute_covariance(self):

~/env/lib/python3.6/site-packages/scipy/stats/kde.py in _compute_covariance(self)
    564                                                bias=False,
    565                                                aweights=self.weights))
--> 566             self._data_inv_cov = linalg.inv(self._data_covariance)
    567 
    568         self.covariance = self._data_covariance * self.factor**2

~/env/lib/python3.6/site-packages/scipy/linalg/basic.py in inv(a, overwrite_a, check_finite)
    972         inv_a, info = getri(lu, piv, lwork=lwork, overwrite_lu=1)
    973     if info > 0:
--> 974         raise LinAlgError("singular matrix")
    975     if info < 0:
    976         raise ValueError('illegal value in %d-th argument of internal '

LinAlgError: singular matrix

• OS: 10.14.6
• Python: 3.6.8.final.0
• pd: 0.25.1
• np: 1.17.2
• sns: 0.9.0