Introduction to R - Part 2 (COMPLETE)

FRONT

BACK

FIRST PASS

FIRST PASS

SECOND PASS

SECOND PASS

What are the arguments for data frames and what do they do?

Data frames have six arguments:

1. The data

2. row.names

3. check.rows: Fixes rare instances where rows can have inconsistent lengths or faulty names without producing an error

4. check.names: Corrects column names if they are incompatible or duplicates

5. fix.empty.names: Gives columns with no names a name

6. stringsAsFactors: Whether to autoconvert character vectors to factors

How do you change the levels of a factor?

levels(factor) <- c(x)

What are the arguments for factors and what do they do?

There are 6 arguments:

1. x - the data

2. levels - buckets to match the data to

3. labels - relabels the buckets from the data names

4. exclude - what data you want to exclude, (makes them NA)

5. ordered - (whether or not the levels are hierarchical)

6. nmax - (maximum number of levels)

What’s the difference between the str() and summary() function?

str() tells you about what’s inside the object, summary() gives you statistical information about the object

What are the two ways you can select list elements other than through numbers?

There are two ways. First through double brackets with the label. Second with a dollar sign.

Ex1: list[[“label”]]

Ex2: list$label

What function allows you to select rows from a dataframe that meet a specific column condition? What are its arguments?

subset(dataframe, condition)

What is a factor?

A statistical data type used to store categorical variables

How do you create a factor?

x <- factor(vector)

How do you get the levels of a factor?

levels(factor)

How are factor levels automatically ordered if you don’t specify them?

Alphabetically

What function gives you a statistical overview of the contents of an object/variable?

summary()

What happens if you try to compare unordered factors?

You get a warning

Are factors unordered or ordered by default?

Unordered

Do factors order from least to greatest, or greatest to least?

Least to greatest

How do you access a specific cell from a factor?

factor[x]

What is the function to create a data frame?

data.frame()

What is the main difference between a matrix and a data frame?

Data frames can contain many different types of data at the same time, where matrices only contain data of the same type

What functions print the first 6 and last 6 lines of data from a data frame or matrix?

head() and tail()

What function shows you the structure of an object?

str()

Can data frames have identical row names?

Not usually

What is a good way to remember how you select data frame elements?

Same as matrix selection

Are there any ways you can select data frame elements other than through numbers? If so, provide an example.

Yes, you can select them through the labels of the rows or columns.

Ex: matrix[1, “label”]

How can you select all of the elements of a column in a dataframe without using brackets?

dataframe$columnname

What happens if you pass a boolean vector as one of the bracket arguments of a dataframe?

You return a dataframe with only the elements in that row or column that are true

What function sorts data from least to greatest?

order()

What function is like a vector, but can carry different variable types?

list()

How do you name a list’s rows while initializing them?

list(name1 = x, name2 = y)

Can you name vectors?

Yes

What’s the difference between single brackets and double brackets for lists?

The single bracket returns the container (a list), the double bracket returns the actual element inside the container

How do you select a specific element FROM a specific element, from a list?

list[[x]][y]

Why don’t dataframes have an argument for the column names?

The labels of the data used to create the dataframe become the column names automatically