DESCRIPTION

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question box to the answer box.

QUESTION -ext .R -run 'Rscript omsi_answer1.txt'

(25 pts, text) In grading Homework I, the TA will first load rectools,
then load your predict.usrData() function, replacing the one that was
included in rectools.  She could avoid such replacement, i.e. keep the
old version and still have a new version, by giving a different name to
your function, say predict.usrData1().  But this would cause problems in
prediction.  Explain.

QUESTION -ext .R -run 'Rscript omsi_answer2.R'

(25 pts, code) Here you write code that will first load the InstEval
dataset and then print the number of users who rated instructor number 36.
Fill in the blanks:

library(rectools)



print(     )  # should print 21

QUESTION -ext .R -run 'Rscript omsi_answer3.R'

(25 pts, text) Consider the InstEval data. Suppose we were to call
prcomp() on ivl[,-(1:2)], and decide to use 3 principal components, i.e.
use the eigenvectors corresponding to the 3 largest eigenvalues. State
how many rows and columns the matrix R would have in Equation (2.26).
Note: You may find you need to use the fact that there are 73421 rows in
ivl.

QUESTION -ext .R -run 'Rscript omsi_answer4.R'

(25 pts, code) In this problem you will write a function with call form

meanActivity(db)

where db is the database returned by formUserData().  The return value
is the average number of ratings, across all users.

Fill in the blanks (or, for partial credit, write your own code with the
same call form and return value).

meanActivity <- function(db) {
   tmp <- sapply(    , function(dbElement)        )

}

library(rectools) 
d <- data.frame(uID=c(1,2,1),iID=c(5,1,8),rat=c(3,3,5)) 
db <- formUserData(d)
print(meanActivity(db))  # should print 1.5