I have a data frame with several columns; some numeric and some character. How to compute the sum of a specific column? I’ve googled for this and I see numerous functions (sum, cumsum, rowsum, rowSums, colSums, aggregate, apply) but I can’t make sense of it all.

For example, suppose I have a data frame people with the following columns

Name Height Weight

Mary 65 110

John 70 200

Jane 64 115

…

How do I get the sum of all the weights?