Applying a function to each couple of elements of a column in a pandas data frame

Question

I have the need to create a new column of a pandas data frame applying a function to each couple of consecutive elements.The first element if the new column has to be a nan. Let's assume that the function is the sum of the elements divided by 3. Here's an example to clarify what I need:

a b new_column
1 2 nan
3 4 2
5 5 3

Answer 1

# We are going to assign a new column
df = df.assign(
    # based on a function that we will apply
    new_column = df.apply(
        # the function adds each value in column a and b and divide it by 3 (without rest)
        lambda row: (row["a"] + row["b"]) // 3, axis = 1
    )
)

# Finally we delete our first entry
df["new_column"][0] = ""