Often you have to create new variables by aggregating across columns or variables. These aggregations can be averages or sums.

You also sometimes have to create a new variable that shows the maximum, minimum, median, or standard deviation of a set of columns (variables) for each individual case (row).

You can also combine string variables together using a concatenate function or look a row ahead or behind using a lag function.

As with everything in R, there are multiple ways to accomplish these tasks. Here are a couple of ways to compute new variables by working in a row (i.e., across columns) to compute a new value for each row in a data frame.