Axis must have `freq` set to convert to Periods | Seasonal_Decompose

Question

I have a temp DF that has the following data in it

Quarter
2016Q3    146660510.0
2016Q4    123641451.0
2017Q1    125905843.0
2017Q2    129656327.0
2017Q3    126586708.0
2017Q4    116804168.0
2018Q1    118167263.0
2018Q2    121633740.0
2018Q3    125314447.0
2018Q4    120994896.0
2019Q1    126124709.0
2019Q2    134753318.0

I'm passing this into seasonal_decompose as quarterly data as per below but I get an error messsage saying "Axis must have freq set to convert to Periods". Frequency has been set in the DF. I think the issue is related to the fact you have to specify to matplotlib that the x axis is periods but I don't know how to do that and can't find any other examples where a DecomposeResult object with quarters is used

result = seasonal_decompose(temp, model='additive',period=4)  
result.plot()
plt.show()

Answer 1

Just convert your PeriodIndex to a DatetimeIndex, that will solve the issue:

    df.index = df.index.to_timestamp()

Answer 2

 date=['2016Q3'
 ,'2016Q4'
 ,'2017Q1'
 ,'2017Q1'
 ,'2017Q3'
 ,'2017Q4'
 ,'2018Q1'
 ,'2018Q3'
 ,'2018Q3'
 ,'2018Q4'
 ,'2019Q1'
 ,'2019Q2']

 data=[146660510.0
 ,123641451.0
 ,125905843.0
 ,129656327.0
 ,126586708.0
 ,116804168.0
 ,118167263.0
 ,121633740.0
 ,125314447.0
 ,120994896.0
 ,126124709.0
 ,134753318.0]

 df=pd.DataFrame({'date':date,'data':data})
 df['date']=pd.to_datetime(df['date'])
 df=df.set_index('date')
 ax=df.plot(figsize=(14,2))
 plt.show()

 decomposition=sm.tsa.seasonal_decompose(x=df['data'],model='additive',      extrapolate_trend='freq', period=3)

 decomposition_trend=decomposition.trend
 ax= decomposition_trend.plot(figsize=(14,2))
 ax.set_xlabel('Date')
 ax.set_ylabel('Trend of time series')
 ax.set_title('Trend values of the time series')
 plt.show()

 decomposition_residual=decomposition.resid
 ax= decomposition_residual.plot(figsize=(14,2))
 ax.set_xlabel('Date')
 ax.set_ylabel('Residual of time series')
 ax.set_title('Residual values of the time series')
 plt.show()