Simple heatmap with 2 1D columns as x and y-axis, and 1 1D column as z-axis

Question

I have the dataframe with x- and y-axis coordinates and z-values:

df = pd.DataFrame({\'x\':[1,2,2,3,3,3],\'y\':[1,1,2,1,2,3],\'z\':[3,2,4,5,1,6]})
df