Extracting value that meets 2 conditions in r

Question

I have a data set and I want to extract the restaurant name by rating and state. I want to write a function with two arguments: state and rating.

> rest_data
  restaurant_name rating state  visitors_per_day
1          a      3.4    NY           34
2          b      5.0    CA           20
3          c      4.0    NY           11 
4          d      4.3    AZ           34 
5          e      4.9    NY           14
6          f      3.0    CA           21 

This is how I should call the function: state name and the rating

my_function("NY", 4.9)

I tried various ways but I was only able to extract using 1 argument.

Thank you

Answer 1

Something like this maybe:

get_rest <- function(state, rating) {
  rest_data[rest_data$state == state & rest_data$rating == rating, 'restaurant_name']
}

get_rest('NY', 4.9)
#[1] e

And actually this is a much better way to test it:

#almost equal is a vectorised form of all.equal that
#checks if two numbers are equal but with a tolerance level
#because of the inconistenies of storing numbers in a computer
#check: http://stackoverflow.com/questions/9508518/why-are-these-numbers-not-equal
#for details
almost.equal <- function (x, y, tolerance=.Machine$double.eps^0.5,
                          na.value=TRUE)
{
  answer <- rep(na.value, length(x))
  test <- !is.na(x)
  answer[test] <- abs(x[test] - y) < tolerance
  answer
} 

get_rest <- function(state, rating) {
  rest_data[rest_data$state == state & almost.equal(rest_data$rating, rating),
            'restaurant_name']
}

get_rest('NY', 4.9)
#[1] e

I have stolen almost.equal from here