Loop with two dimensions

[Ioanna]

Hello! I have a data frame where the first column contains dates, the second one names and the other two earnings and costs. I want to make a for loop that will calculate the difference between earnings and costs for every name and every date. I have managed to do it for every name but when I try to expand it for every date I am not able to do it. In my loop I assume that i is the date and k is the name so the difference will be for example earnings [i,k] - costs [i,k] but I get the message that there is something wrong with the dimensions.

[nirgrahamuk]

I wouldn't think to use a loop for this . r is vectorised language.
in base R to find the difference between Petal.Length and Petal.Width for each observation in iris

iris$diff <- iris$Petal.Length - iris$Petal.Width

with library(tidyverse)

iris <- mutate(iris, diff = Petal.Length - Petal.Width)

[siddharthprabhu]

In future, please try to provide sample data in an easy-to-copy format (as I have done in the code below). This makes it much easier for others to help you.

As nirgrahamuk pointed out, R is vectorized so you don't need loops for these kind of operations. You can directly assign the result of the computation to a new variable.

df <- data.frame(stringsAsFactors = FALSE,
                 date = c(as.Date("2020-07-01"), as.Date("2020-07-02")),
                 name = c("John", "Mary"),
                 earnings = c(1500, 2000),
                 cost = c(1250, 1500))

df$difference <- df$earnings - df$cost

df
#>         date name earnings cost difference
#> 1 2020-07-01 John     1500 1250        250
#> 2 2020-07-02 Mary     2000 1500        500

^{Created on 2020-07-31 by the reprex package (v0.3.0)}

[Ioanna]

Thank you! My issue was that for a particular date I had many names which were the same so the difference could not be calculated that easily however now everything works ok!