Reshaping, joining and visualisation data

Question 1

function to do summarising and filtering by subgroups of the data.

Answer 1

group_by()

Question 1

There are two main types of join

Answer 1

Mutating joins add new columns from the additional dataset.

Filtering joins filter out existing columns based on information in the additional dataset.

Question 2

There are four separate mutating joins

Answer 2

left_join(x,y) returns all rows in x, and all rows that match these in y. If y doesn’t have a match, NA will be used.

right_join(x,y) returns all rows in y and all rows that match these in x. If x doesn’t have a match in y, NA will be used.

inner_join(x,y) returns only rows in x and y that have a match.

full_join(x,y) returns all rows in x and all rows in y. Anything in x or y that don’t have a match will be filled with NA.

Question 3

There are three interrelated rules which make a dataset tidy

Answer 3

1. Each variable should be a column.
2. Each observation should be a row.
3. Each value should have its own cell