If value in column A is true or equal take the value from Column B

Question

```Class       Grade
   Physics       8
   Math          7
   English       7.5
   Biology       5 
   Physics       4

if(Class == Physics) {Sum(Grade)

I am looking that when the Class is similar to what I am searching it takes the Grade next to it. I assume something like this. and it will combine so in this case 12 for physics. And then That I can create a new dataframe where I can combine all the numbers corresponding to the Class.

Does this function combine all Physics = 12, Math =7, English 7,5 together? — Sjors Hendrikx, Jul 02 '20 at 08:06

score 0 · Accepted Answer · answered Jul 02 '20 at 08:27

0

A data.table solution for this.

df = data.frame(Class = c("Physics", "Math", "English", "Biology", "Physics"),
                Grade = c(8, 7, 7.5, 5, 4))

library(data.table)
setDT(df)
df[, sum(Grade), by =  Class]

answered Jul 02 '20 at 08:27

ljwharbers

393
2
8

If value in column A is true or equal take the value from Column B

1 Answers1