[R] Finding unique terms

[Dénes Tóth]

On 10/12/2018 04:36 AM, Jeff Newmiller wrote:
> You said "add up"... so you did not mean to say that? Denes computed the mean...

Nice catch, Jeff. Of course I wanted to use 'sum' instead of 'mean'.


> 
> On October 11, 2018 3:56:23 PM PDT, roslinazairimah zakaria <roslinaump using gmail.com> wrote:
>> Hi Denes,
>>
>> It works perfectly as I want!
>>
>> Thanks a lot.
>>
>> On Fri, Oct 12, 2018 at 6:29 AM Dénes Tóth <toth.denes using kogentum.hu>
>> wrote:
>>
>>>
>>>
>>> On 10/12/2018 12:12 AM, 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.
>>>
>>> dat <- 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 assume you would like to add up the values with na.rm = TRUE
>>> meanFn <- function(x) mean(x, na.rm = TRUE)
>>>
>>> # see ?aggregate
>>> aggregate(dat[, c("PO1M", "PO1T", "PO2M")],
>>>             by = dat["STUDENT_ID"],
>>>             FUN = meanFn)
>>>
>>> # if you have largish or large data
>>> library(data.table)
>>> dat2 <- as.data.table(dat)
>>> dat2[, lapply(.SD, meanFn),
>>>        by = STUDENT_ID,
>>>        .SDcols = c("PO1M", "PO1T", "PO2M")]
>>>
>>>
>>> Regards,
>>> Denes
>>>
>>>
>>>>
>>>> How do I do that?
>>>> Thank you for any help given.
>>>>
>>>
>