Reshape the data so rows are indexed by animal, columns are the distinct visits values, and each cell holds the mean age for that animal/visits combination.

Input

  animal  age  visits priority
a    cat  2.5       1      yes
b    cat  3.0       3      yes
c  snake  0.5       2       no
d    dog  NaN       3      yes
e    dog  5.0       2       no
f    cat  2.0       3       no
g  snake  4.5       1       no
h    cat  NaN       1      yes
i    dog  7.0       2       no
j    dog  3.0       1       no

Output

visits    1    2    3
animal               
cat     2.5  NaN  2.5
dog     3.0  6.0  NaN
snake   4.5  0.5  NaN