Encountered invalid value when I use pearsonr

Question

Maybe I made a mistake. If so, I am sorry to ask this.

I want to calculate Pearson\'s correlation coefficent by using scipy\'s pearsonr function.

Answer 1

Pearson's correlation coefficient between two variables is defined as the covariance of the two variables divided by the product of their standard deviations.

So it's the covariance over

• the standard deviation of [4, 5, 5, 4, 4, 4] times
• the standard deviation of [4, 4, 4, 4, 4, 4].

The standard deviation of [4, 4, 4, 4, 4, 4] is zero.

So it's the covariance over

• the standard deviation of [4, 5, 5, 4, 4, 4] times
• zero.

So it's the covariance over

• zero.

Anything divided by zero is nan. The value of the covariance is irrelevant.