Question

I need to know how to use R to count certain values in a variable. Example design code to look in a table for the variable Cars and count in the rows if they are suburu or ford out of a sample of 15.

Answer 1

#This is just example to introduce you about the concept of data.table and count in r. Actual answer to your question after this section of coding

#Example to illustrate data table in R
#For installing "data.table", use install.packages("data.table")

#library "data.table" is used to create datatable
library(data.table)

#using github repository of cars data
#reading a file
DT <- fread('https://raw.githubusercontent.com/selva86/datasets/master/Cars93_miss.csv')

#initially the cars column is named as "Manufacturer", now I am changing it into "Cars"
print(head(setnames(DT, old = "Manufacturer", new = "Cars")[]))

#Now, let us access "Cars" column and see what are the cars present
print(DT$Cars)

#Counting the frequency of each value of "Cars" column or variable
output <- DT[, .(.N), by = .(Cars)]
print(output)

Code:

Output:

ANSWER:

#Actual answer to your question

#Example to illustrate data table in R
#For installing "data.table", use install.packages("data.table")

#library "data.table" is used to create datatable
library(data.table)

#creating a vector of "Cars" that consits various cars, "topspeed" contains respective TopSpeeds
cars <- c("Audi","Audi","BMW","Chevrolet","Chevrolet","Dodge","Ford","Ford","Ford","Honda","Mazda","Suburu","Suburu","Suburu","Suburu")
topspeed <- c("240","240","195","200","200","220","240","240","240","180","180","260","260","260","260")

#Creating data table that consists cars and their respective topspeeds
dt <- data.table(Cars=cars,TopSpeed=topspeed)
print(dt)

#finding total Cars elements frequency
output <- DT[, .(.N), by = .(Cars)]

#Accessing and finding the count of Ford and suburu
nrow(dt[dt$Cars == "Ford",])
nrow(dt[dt$Cars == "Suburu",])

Code:

Output: