[R] Finding unique terms

[Robert Baer]

On 10/11/2018 5:12 PM, roslinazairimah zakaria wrote:
> Dear r-users,
>
> I have this data:
>
> structure(list(STUDENT_ID = structure(c(1L, 1L, 1L, 1L, 1L, 1L,
> 2L, 2L, 2L, 2L, 2L), .Label = c("AA15285", "AA15286"), class = "factor"),
>      COURSE_CODE = structure(c(1L, 2L, 5L, 6L, 7L, 8L, 2L, 3L,
>      4L, 5L, 6L), .Label = c("BAA1113", "BAA1322", "BAA2113",
>      "BAA2513", "BAA2713", "BAA2921", "BAA4273", "BAA4513"), class =
> "factor"),
>      PO1M = c(155.7, 48.9, 83.2, NA, NA, NA, 48.05, 68.4, 41.65,
>      82.35, NA), PO1T = c(180, 70, 100, NA, NA, NA, 70, 100, 60,
>      100, NA), PO2M = c(NA, NA, NA, 37, NA, NA, NA, NA, NA, NA,
>      41), PO2T = c(NA, NA, NA, 50, NA, NA, NA, NA, NA, NA, 50),
>      X = c(NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA), X.1 = c(NA,
>      NA, NA, NA, NA, NA, NA, NA, NA, NA, NA)), .Names = c("STUDENT_ID",
> "COURSE_CODE", "PO1M", "PO1T", "PO2M", "PO2T", "X", "X.1"), class =
> "data.frame", row.names = c(NA,
> -11L))
>
> I want to combine the same Student ID and add up all the values for PO1M,
> PO1T,...,PO2T obtained by the same ID.
>
> How do I do that?
> Thank you for any help given.
>
oops!  Forgot to clean up after my cut and paste. Solution with dplyr 
looks like this:
# Create sums by student ID
library(dplyr)
dat %>%
   group_by(STUDENT_ID) %>%
   summarize(sum.PO1M = sum(PO1M, na.rm = TRUE),
             sum.PO1T = sum(PO1T, na.rm = TRUE),
             sum.PO2M = sum(PO2M, na.rm = TRUE),
             sum.PO2T = sum(PO2T, na.rm = TRUE))