12.9 Exercise (to do at home)

1- Read in file ex6c_input.txt (that is in folder downloaded for exercice 6 “i_o_files”) in object “extra”

Warning: the file has a header !
Check the structure of extra (remember the str command).

correction

  extra <- read.table("i_o_files/ex6c_input.txt", 
                  header=TRUE)
  str(extra)

2- Read in the same file but, this time, set the argument as.is to TRUE.

Check again the structure: what has changed ?

correction

  extra <- read.table("i_o_files/ex6c_input.txt", 
                  header=TRUE,
                  as.is=TRUE)
  str(extra)

3- What are the column names of extra ?

correction

  colnames(extra)

4- Change the name of the first column of extra from “State” to “Country”.

correction

  # ex6ct all column names of extra
  colnames(extra)
  # ex6ct the name of the first column only
  colnames(extra)[1]
  # reassign name of the first column only
  colnames(extra)[1] <- "Country"

5- How many countries are in the Eurozone, according to extra ?

Remember the table function. ?table

correction

  table(extra$Eurozone)

6- In the Eurozone column: change “TRUE” with “yes” and “FALSE” with “no”.

correction

  # select the Eurozone column
  extra$Eurozone
  # elements of the Eurozone column that are exactly TRUE
  extra$Eurozone==TRUE
  # ex6ct actual values that are TRUE
  extra$Eurozone[extra$Eurozone==TRUE]
  # reassign all elements that are TRUE with "yes"
  extra$Eurozone[extra$Eurozone==TRUE] <- "yes"
  # same with FALSE
  extra$Eurozone[extra$Eurozone==FALSE] <- "no"

7- In the column Country: how many country names from the list contain the letter “c” (capital- or lower-case) ?

Remember the grep function. Check the help page.

correction

  # country names with "c" (lower-case)
  grep("c", extra$Country)
  # country names with "c" or "C" (ignoring case)
  grep("c", extra$Country, ignore.case = TRUE)
  # show actual country names
  grep("c", extra$Country, value=TRUE, ignore.case = TRUE)

8- According to that data frame: how many people live: + in the European union (whole table) ? + in the Eurozone ?

correction

  # sum the whole population column
  sum(extra$Population)
  # select elements of extra where Eurozone is "yes"
  extra$Eurozone == "yes"
  # select only elements in Population for which the corresponding Eurozone elements are "yes"
  extra$Population[extra$Eurozone == "yes"]
  # sum that selection
  sum(extra$Population[extra$Eurozone == "yes"])

9- Write extra into file ex6c_output.txt

After each of the following steps, check the output file in the RStudio file browser (lower-right panel).

• Try with the default arguments.

correction

  write.table(extra, file="ex6c_output.txt")

• Add the argument “row.names” set to FALSE.

correction

  write.table(extra, file="ex6c_output.txt", 
            row.names = FALSE)

• Add the argument “quote” set to FALSE.

correction

  write.table(extra, file="ex6c_output.txt", 
            row.names = FALSE,
            quote = FALSE)

• Add the argument “sep” set to “ or to”,"

correction

  write.table(extra, file="ex6c_output.txt", 
            row.names = FALSE,
            quote = FALSE,
            sep="\t")