Bokeh plot with datetime period (month-year) on x-axis - time-series

Question

I am new to bokeh/pandas and trying to plot a trend line by using month-year for x-axis and integer values for y-axis.
My data looks like below:
year_month emp_count
0 2015-09 1450425
1 2015-10 3093811
2 2015-11 3316241
3 2015-12 3308658
4 2016-01 3402191
To plot using bokeh I am converting both columns to ndarray. When i convert year-month column to ndarray, it shows each value as a Period. I have used to_period('M') method to get year_month out of a date column.
temp_df.year_month.values
>>output
array([Period('2015-09', 'M'), Period('2015-10', 'M'),
Period('2015-11', 'M'), Period('2015-12', 'M'),
Period('2016-01', 'M'), Period('2016-02', 'M'),
So when i plot using this data, i get following error:
TypeError: Object of type 'Period' is not JSON serializable
To avoid this error i converted year_month column type to string but i still get the same error. My complete code looks like below:
temp_df.year_month = temp_df.year_month.astype(str)
output_file('trend1.html')
p = figure(title='Employee trend',
plot_width=800,
plot_height=350,
x_axis_label='Month-Year', y_axis_label='No of Employees',
x_axis_type='datetime')
p.line(x= temp_df.year_month,
y = temp_df.emp_count)
show(p)
Does anyone know how to plot year-month on x-axis using bokeh?

Answer 1

I guess I found the problem. You should convert the column to date time.
df['year_month']=pd.to_datetime(df['year_month'])
This should change your column values to as below (day is defaulted to 01):
year_month emp_count
0 2015-09-01 1450425
1 2015-10-01 3093811
2 2015-11-01 3316241
3 2015-12-01 3308658
4 2016-01-01 3402191
Then the plot would work. I tested it on a dummy value as output is below.
Value month_year
2 2018-11-01
3 2018-01-01
4 2018-02-01
5 2018-05-01
sample=pd.DataFrame(pd.read_csv('sample.csv'))
sample['month_year']=pd.to_datetime(sample['month_year'])
p = figure(title='Employee trend',
plot_width=800,
plot_height=350,
x_axis_label='Month-Year', y_axis_label='No of Employees',
x_axis_type='datetime')
p.scatter(x= sample.month_year,
y = sample.Value)
show(p)
Let me know if this works.
Thanks

Answer 2

I have solved the issue by an alternate approach. Thanks to #Samira for inspiration.
I extracted the year-month from date object and defaulted day to '1'.
df = df.join(df.as_of_date.apply(lambda x : pd.Series({
'day': x.day,
'year':x.year,
'month': x.month,
'year_month': x.to_period('M'),
'year_month_01': pd.datetime(x.year,x.month,1)
})))
After that used 'year_month_01' on axis and bokeh graph looks as expected.
bokeh graph