How to apply loops to multiply across various columns in a dataframe

Question

I have a data frame with the following columns:
sales_1, sales_2, price_1, price_2

Now, I want to calculate revenues by multiplying sales_1 * price_1 and so-on across each number in an iterative manner.

Below is my sample data

sample_data <- data_frame(
  "sales_1" = c(10, 20, 30),
  "sales_2" = c(20, 30, 40),
  "price_1" = c(30, 20, 20),
  "price_2" = c(30, 30, 50))

sample_data
# A tibble: 3 x 4
#  sales_1 sales_2 price_1 price_2
#   <dbl>  <dbl>  <dbl>  <dbl>
#1    10      20      30      30
#2    20      30      20      30
#3    30      40      20      50

I have tried the following code. But this does not work.

sample_data %>%
  mutate (
    for (i in seq_along(1:2)) {
      paste0("total_revenue",i) = paste0("sales_",i) * paste0("price_",i)
    }
  )

Answer 1

I am assuming that your columns are already ordered as (sales_1, sales_2, price_1, price_2)

So now, I would suggest you to split the data frame into 2 parts and then multiply them.

sample_data[grep("sales_", names(sample_data))] * sample_data[grep("price_", names(sample_data))]

#  sales_1 sales_2
#1      300      600
#2      400      900
#3      600     2000

Just in case if you're columns are not sorted according to their names. You can sort them by using order() as follows:

sample_data <- sample_data[order(names(sample_data))]