plot a bar chart using groupby function and plotly and streamlit

Question

i am trying to plot a bar chart based on groupby function but once i try it crash and display the below error:

this error below appear when the user select 3 items from the multiselect widget.

ValueError: All arguments should have the same length. The length of argument color is 3, whereas the length of previously-processed arguments ['gender', 'count'] is 95

code:

some_columns_df = df.loc[:,['gender','country','city','hoby','company','status']]
some_collumns = some_columns_df.columns.tolist()

select_box_var= st.selectbox("Choose X Column",some_collumns)
multiselect_var= st.multiselect("Select Columns To GroupBy",some_collumns)  

test_g3 = df.groupby([select_box_var] + multiselect_var).size().reset_index(name='count')
fig = px.histogram(test_g3,x=select_box_var, y='count',color=multiselect_var ,barmode = 'group',text_auto = True)

            

I know the error is in the color parameter in the px.histogram

Answer 1

The reason is color only accepts one category.

color=['column_a','column_b']

Would cause

ValueError: All arguments should have the same length. The length of argument color is 2, whereas the length of previously-processed arguments ['total_bill'] is 244

2 is the length of list ['column_a','column_b'], while 244 is the dataframe's rows.

According to the document:

color (str or int or Series or array-like) – Either a name of a column in data_frame, or a pandas Series or array_like object. Values from this column or array_like are used to assign color to marks.

Therefore, either we use a column_name, or we use a series. Here's my approach:

import plotly.express as px
df = px.data.tips() # a data set from plotly
df.head()

Output

  total_bill   tip     sex smoker  day    time  size
0       16.99  1.01  Female     No  Sun  Dinner     2
1       10.34  1.66    Male     No  Sun  Dinner     3
2       21.01  3.50    Male     No  Sun  Dinner     3
3       23.68  3.31    Male     No  Sun  Dinner     2
4       24.59  3.61  Female     No  Sun  Dinner     4

Column:
sex with unique values Female and Male

time with unique values Dinner and Lunch I choose these two columns, it's easier to figure out that there is only 4 combination.

We create a series that concat columns sex and time

categories = df[['sex','time']].agg(', '.join, axis=1)
print(categories)

Output

0      Female, Dinner
1        Male, Dinner
2        Male, Dinner
3        Male, Dinner
4      Female, Dinner
            ...      
239      Male, Dinner
240    Female, Dinner
241      Male, Dinner
242      Male, Dinner
243    Female, Dinner
Length: 244, dtype: object

---

Utilize this categories as color reference

fig = px.histogram(df, x="total_bill", color =categories)
fig.show()

---

If ','.join didn't work, having issue,

categories = df[['sex','time']].agg(', '.join, axis=1)

then we try another way

categories = df['sex'] + df['time']

Sup[1]