Advanced Data Processing

Question 1

apply(X,INDEX,FUN=)

Answer 1

a vector or array or list of values obtained by applying a function FUN to margins (INDEX) of X

Question 2

lapply(X,FUN)

Answer 2

apply FUN to each element of the list X

Question 3

tapply(X,INDEX,FUN=)

Answer 3

apply FUN to each cell of a ragged array given

by X with indexes INDEX

Question 4

by(data,INDEX,FUN)

Answer 4

apply FUN to data frame data subsetted by INDEX

Question 5

merge(a,b)

Answer 5

merge two data frames by common columns or row names

Question 6

xtabs(a b,data=x)

Answer 6

a contingency table from cross-classifying factors

Question 7

aggregate(x,by,FUN)

Answer 7

splits the data frame x into subsets, computes
summary statistics for each, and returns the result in a convenient form; by is a list of grouping elements, each as long as the variables in x

Question 8

stack(x, …)

Answer 8

transform data available as separate columns in a data frame or list into a single column

Question 9

unstack(x, …)

Answer 9

inverse of stack()

Question 10

reshape(x, …)

Answer 10

reshapes a data frame between ’wide’ format with
repeated measurements in separate columns of the same record and ’long’ format with the repeated measurements in separate records; use (direction=”wide”) or (direction=”long”)