### Regression

To represent the two variables, we can perform a 2d histogram.


Then we could look at the histogram of $z_2$ for a given class of $z_1$.

For instance, if we consider the 3rd class, $z_1\in[1.14,1.67]$ :





It shows the conditional distribution of $z_2$ knowing that $z_1\in[1.14,1.67]$.

#### Conditional mean (or regression)

In the same spirit, we can consider the conditional mean (mean of $z_2$ for different class of $z_1$). 

It is named conditional mean (or regression).