Creating Data Frames

Part of the Logic & Flow section of Coddy's R journey. Lesson 42 of 64.

A data frame is R's table: every column is a vector with its own type, and all columns have the same length, one value per row. data.frame() builds one from named vectors:

people <- data.frame(
  name = c("ada", "bo", "cy"),
  age = c(36, 22, 41),
  city = c("london", "paris", "rome")
)
print(people)

Output:

  name age   city
1  ada  36 london
2   bo  22  paris
3   cy  41   rome

nrow() and ncol() give the size, and names() lists the columns. Unlike a matrix, the columns can hold different types: here text and numbers.

people <- data.frame(
  name = c("ada", "bo", "cy"),
  age = c(36, 22, 41),
  city = c("london", "paris", "rome")
)
print(nrow(people))
print(ncol(people))
print(names(people))

Output:

[1] 3
[1] 3
[1] "name" "age"  "city"

str() shows the type and the first values of every column, which is a quick way to check what a data frame holds:

people <- data.frame(
  name = c("ada", "bo", "cy"),
  age = c(36, 22, 41),
  city = c("london", "paris", "rome")
)
str(people)

Output:

'data.frame':	3 obs. of  3 variables:
 $ name: chr  "ada" "bo" "cy"
 $ age : num  36 22 41
 $ city: chr  "london" "paris" "rome"

Data often arrives as text with one row per line. read.csv(text = lines) turns such lines into a data frame, using the first line as the column names and converting numbers automatically:

lines <- c("item,qty", "tea,2", "jam,5")
orders <- read.csv(text = lines)
print(orders)
print(sum(orders$qty))

Output:

  item qty
1  tea   2
2  jam   5
[1] 7

Challenge

Easy

Complete table_info(names, ages). Build a data frame with the columns name and age from the two vectors. Return three lines: Rows: with the number of rows, Columns: with the column names joined by , , and Oldest: with the name in the row with the largest age (the first one when ages tie).

The supplied code reads the names and the ages as two comma-separated lines and prints each returned line.

Try it yourself

table_info <- function(names, ages) {
  # Write your code here
  character(0)
}

# Supplied input/output code: keep it as it is
input <- suppressWarnings(readLines(file("stdin")))
cat(table_info(strsplit(input[1], ",")[[1]], as.numeric(strsplit(input[2], ",")[[1]])), sep = "\n")