Perfect!
Now, let's display the starting point of each transportation company. The starting point is denoted with a zero in the destination_number column. Here's an example using company_a:
| city | country | ... | destination_number | ... | |
|---|---|---|---|---|---|
| 1 | Prague | Czech Republic | ... | 0 | ... |
First, let's create a function named starting_point that takes a single data frame named df and returns the name of the city for which destination_number is equal to zero.
Hint 1: df$destination_number and df$city will extract the destination_number and city columns, respectively.
Hint 2: You can extract all rows for which destination_number equals 0 like this:
df[df$destination_number == 0, ]
Hint 3: To display only the city column, use this code:
df[df$destination_number == 0, "city"]
