12.8 Exercise 7: Library and packages

Create the script “exercise7.R” and save it to the “Rcourse/Module2” directory: you will save all the commands of exercise 7 in that script.
Remember you can comment the code using #.

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getwd()
setwd("Rcourse/Module2")
setwd("~/Rcourse/Module2")

1- Install and load the packages ggplot2 and WriteXLS

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# Install the 2 packages at once
install.packages(pkgs=c("ggplot2", "WriteXLS"))
# Load in the environment (one by one)
library("ggplot2")
library("WriteXLS")

Check with sessionInfo() that the packages were loaded.

2- ggplot2 loads automatically the diamonds dataset in the working environment: you can use it as an object after ggplot2 is loaded.

What are the dimensions of diamonds? What are the column names of diamond?

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# Dimensions of diamonds
dim(diamonds)
# Column names of diamonds
colnames(diamonds)

You can read the help page of the diamonds dataset to understand what it contains!

Note: diamonds is a data frame: you can test it with is.data.frame(diamonds) (returns TRUE).

3- Select the columns carat, cut, color and price of diamonds and store in the object diams1.

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# Select columns
diams1 <- diamonds[,c("carat", "cut", "color", "price")]

4- Install and load the package dplyr from the Console.

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# Install package
install.packages(pkgs="dplyr")
# Load package
library("dplyr")

5- Use the function “sample_n” from the dplyr package to randomly sample 200 lines of diams1: save in diams object.

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# Subset data frame
diams <- sample_n(tbl=diams1, size=200)

6- Save diams into 2 files (different file formats):

• diamonds200.txt with function write.table (from package utils)
• diamonds200.xls with function WriteXLS (from package of the same name WriteXLS).

Note: read about and play with the different options of both functions and check the output files.

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# Write a text file with write.table
write.table(x=diams, 
    file="diamonds200.txt",
        row.names=FALSE,
        quote=FALSE,
        sep="\t")
# Write an Excel file with WriteXLS
WriteXLS(x=diams, 
    ExcelFileName="diamonds200.xls", 
    row.names=FALSE, 
    col.names=TRUE, 
    FreezeRow=1, 
    BoldHeaderRow=TRUE)