Question about autocorrelation_plot result vs autocorr result





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I used autocorrelation_plot to plot the autocorrelation of a straight line:



import numpy as np
import pandas as pd
from pandas.plotting import autocorrelation_plot
import matplotlib.pyplot as plt

dr = pd.date_range(start='1984-01-01', end='1984-12-31')

df = pd.DataFrame(np.arange(len(dr)), index=dr, columns=["Values"])
autocorrelation_plot(df)
plt.show()


enter image description here



Then, I tried using autocorr() to calculate the autocorrelation with different lags:



for i in range(0,366):
print(df['Values'].autocorr(lag=i))


The output is 1 (or 0.99) for all the lag. But it is clear from the correlogram that the autocorrelation is a curve rather than a straight line fixed at 1.



Did I interpret the correlogram incorrectly or did I use the autocorr() function incorrectly? Thanks!










share|improve this question































    1















    I used autocorrelation_plot to plot the autocorrelation of a straight line:



    import numpy as np
    import pandas as pd
    from pandas.plotting import autocorrelation_plot
    import matplotlib.pyplot as plt

    dr = pd.date_range(start='1984-01-01', end='1984-12-31')

    df = pd.DataFrame(np.arange(len(dr)), index=dr, columns=["Values"])
    autocorrelation_plot(df)
    plt.show()


    enter image description here



    Then, I tried using autocorr() to calculate the autocorrelation with different lags:



    for i in range(0,366):
    print(df['Values'].autocorr(lag=i))


    The output is 1 (or 0.99) for all the lag. But it is clear from the correlogram that the autocorrelation is a curve rather than a straight line fixed at 1.



    Did I interpret the correlogram incorrectly or did I use the autocorr() function incorrectly? Thanks!










    share|improve this question



























      1












      1








      1








      I used autocorrelation_plot to plot the autocorrelation of a straight line:



      import numpy as np
      import pandas as pd
      from pandas.plotting import autocorrelation_plot
      import matplotlib.pyplot as plt

      dr = pd.date_range(start='1984-01-01', end='1984-12-31')

      df = pd.DataFrame(np.arange(len(dr)), index=dr, columns=["Values"])
      autocorrelation_plot(df)
      plt.show()


      enter image description here



      Then, I tried using autocorr() to calculate the autocorrelation with different lags:



      for i in range(0,366):
      print(df['Values'].autocorr(lag=i))


      The output is 1 (or 0.99) for all the lag. But it is clear from the correlogram that the autocorrelation is a curve rather than a straight line fixed at 1.



      Did I interpret the correlogram incorrectly or did I use the autocorr() function incorrectly? Thanks!










      share|improve this question
















      I used autocorrelation_plot to plot the autocorrelation of a straight line:



      import numpy as np
      import pandas as pd
      from pandas.plotting import autocorrelation_plot
      import matplotlib.pyplot as plt

      dr = pd.date_range(start='1984-01-01', end='1984-12-31')

      df = pd.DataFrame(np.arange(len(dr)), index=dr, columns=["Values"])
      autocorrelation_plot(df)
      plt.show()


      enter image description here



      Then, I tried using autocorr() to calculate the autocorrelation with different lags:



      for i in range(0,366):
      print(df['Values'].autocorr(lag=i))


      The output is 1 (or 0.99) for all the lag. But it is clear from the correlogram that the autocorrelation is a curve rather than a straight line fixed at 1.



      Did I interpret the correlogram incorrectly or did I use the autocorr() function incorrectly? Thanks!







      python pandas autocorrelation






      share|improve this question















      share|improve this question













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      share|improve this question








      edited Jan 3 at 10:22







      Cheng

















      asked Jan 3 at 7:15









      ChengCheng

      6,39784070




      6,39784070
























          1 Answer
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          active

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          1














          You are using both functions correctly, but... Autocorrelation_plot uses a different way of calculating autocorrelations then autocorr() does.

          The following two posts explain more about the differences. Unfortunately I don't know which way of calculating is the correct way:



          What's the difference between pandas ACF and statsmodel ACF?



          Why NUMPY correlate and corrcoef return different values and how to "normalize" a correlate in "full" mode?



          If you need it, you can get the autocorrelations out of your autocorrelation plot as follows:



          ax = autocorrelation_plot(df)
          ax.lines[5].get_data()[1]





          share|improve this answer


























          • Thanks for the links. From what I can tell, autocorr() called np.corrcoef() which calculates the pearson correlation, which is different from autocomplete correlation. The implementation of autocorrelation_plot is correct. I have submitted an issue on github.

            – Cheng
            Jan 4 at 8:54












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          1 Answer
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          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          1














          You are using both functions correctly, but... Autocorrelation_plot uses a different way of calculating autocorrelations then autocorr() does.

          The following two posts explain more about the differences. Unfortunately I don't know which way of calculating is the correct way:



          What's the difference between pandas ACF and statsmodel ACF?



          Why NUMPY correlate and corrcoef return different values and how to "normalize" a correlate in "full" mode?



          If you need it, you can get the autocorrelations out of your autocorrelation plot as follows:



          ax = autocorrelation_plot(df)
          ax.lines[5].get_data()[1]





          share|improve this answer


























          • Thanks for the links. From what I can tell, autocorr() called np.corrcoef() which calculates the pearson correlation, which is different from autocomplete correlation. The implementation of autocorrelation_plot is correct. I have submitted an issue on github.

            – Cheng
            Jan 4 at 8:54
















          1














          You are using both functions correctly, but... Autocorrelation_plot uses a different way of calculating autocorrelations then autocorr() does.

          The following two posts explain more about the differences. Unfortunately I don't know which way of calculating is the correct way:



          What's the difference between pandas ACF and statsmodel ACF?



          Why NUMPY correlate and corrcoef return different values and how to "normalize" a correlate in "full" mode?



          If you need it, you can get the autocorrelations out of your autocorrelation plot as follows:



          ax = autocorrelation_plot(df)
          ax.lines[5].get_data()[1]





          share|improve this answer


























          • Thanks for the links. From what I can tell, autocorr() called np.corrcoef() which calculates the pearson correlation, which is different from autocomplete correlation. The implementation of autocorrelation_plot is correct. I have submitted an issue on github.

            – Cheng
            Jan 4 at 8:54














          1












          1








          1







          You are using both functions correctly, but... Autocorrelation_plot uses a different way of calculating autocorrelations then autocorr() does.

          The following two posts explain more about the differences. Unfortunately I don't know which way of calculating is the correct way:



          What's the difference between pandas ACF and statsmodel ACF?



          Why NUMPY correlate and corrcoef return different values and how to "normalize" a correlate in "full" mode?



          If you need it, you can get the autocorrelations out of your autocorrelation plot as follows:



          ax = autocorrelation_plot(df)
          ax.lines[5].get_data()[1]





          share|improve this answer















          You are using both functions correctly, but... Autocorrelation_plot uses a different way of calculating autocorrelations then autocorr() does.

          The following two posts explain more about the differences. Unfortunately I don't know which way of calculating is the correct way:



          What's the difference between pandas ACF and statsmodel ACF?



          Why NUMPY correlate and corrcoef return different values and how to "normalize" a correlate in "full" mode?



          If you need it, you can get the autocorrelations out of your autocorrelation plot as follows:



          ax = autocorrelation_plot(df)
          ax.lines[5].get_data()[1]






          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Jan 3 at 12:50

























          answered Jan 3 at 12:43









          Sander van den OordSander van den Oord

          715520




          715520













          • Thanks for the links. From what I can tell, autocorr() called np.corrcoef() which calculates the pearson correlation, which is different from autocomplete correlation. The implementation of autocorrelation_plot is correct. I have submitted an issue on github.

            – Cheng
            Jan 4 at 8:54



















          • Thanks for the links. From what I can tell, autocorr() called np.corrcoef() which calculates the pearson correlation, which is different from autocomplete correlation. The implementation of autocorrelation_plot is correct. I have submitted an issue on github.

            – Cheng
            Jan 4 at 8:54

















          Thanks for the links. From what I can tell, autocorr() called np.corrcoef() which calculates the pearson correlation, which is different from autocomplete correlation. The implementation of autocorrelation_plot is correct. I have submitted an issue on github.

          – Cheng
          Jan 4 at 8:54





          Thanks for the links. From what I can tell, autocorr() called np.corrcoef() which calculates the pearson correlation, which is different from autocomplete correlation. The implementation of autocorrelation_plot is correct. I have submitted an issue on github.

          – Cheng
          Jan 4 at 8:54




















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