Question

Four important functions used in dplyr to merge two datasets.

Answer 1

Function	Objectives	Arguments	Multiple keys
left_join()	Merge two datasets. Keep all observations from the origin table	data, origin, destination, by = "ID"	origin, destination, by = c("ID", "ID2")
right_join()	Merge two datasets. Keep all observations from the destination table	data, origin, destination, by = "ID"	origin, destination, by = c("ID", "ID2")
inner_join()	Merge two datasets. Excludes all unmatched rows	data, origin, destination, by = "ID"	origin, destination, by = c("ID", "ID2")
full_join()	Merge two datasets. Keeps all observations	data, origin, destination, by = "ID"	origin, destination, by = c("ID", "ID2")

Using the tidyr Library you can transform a dataset with the gather(), spread(), separate() and unit() functions.

Function	Objectives	Arguments
gather()	Transform the data from wide to long	(data, key, value, na.rm = FALSE)
spread()	Transform the data from long to wide	(data, key, value)
separate()	Split one variables into two	(data, col, into, sep= "", remove = TRUE)
unit()	Unit two variables into one	(data, col, conc ,sep= "", remove = TRUE)