R/followersCount.R

In tangaot/twitterapiR: An R Wrapper for the Twitter API

followersCount <- function(screen_name){
    #' followersCount
    #' 
    #' @description This function will accept the screen name of a user and output the total number of followers of that user
    #' 
    #' @param screen_name character. A string of one Twitter screen name. 
    #' 
    #' @usage followersCount(screen_name)
    #' @return A DataFrame containing the following columns:
    #' screen_name: The screen name of a user
    #' followers_count: The number of followers of a user
    #' 
    #' @references <https://developer.twitter.com/en/docs/twitter-api/v1/accounts-and-users/follow-search-get-users/api-reference/get-followers-list>
    #' @examples
    #' followersCount(screen_name ="BarackObama")
    #' 
    #' @export
    #' 
    
    # raise an error if the number of characters of the inputted screen name is greater than 100 and if the number of characters of the inputted screen name is 0.
    if (nchar(screen_name) > 100) {
        stop("screen_name can only be up to 100 characters")
    } else if (nchar(screen_name) == 0) {
        stop("screen_name cannot be empty")
    }
    
    # get the bearer key
    bearer = get_bearer()

    # retrieve information from Twitter
    screen_name <- utils::URLencode(screen_name, reserved = TRUE) # encode characters in URLs
    base <- "https://api.twitter.com/1.1/users/show.json?screen_name="
    url <- paste0(base, screen_name)
    res = httr::GET(url, httr::add_headers(Authorization=paste0("Bearer ", bearer$access_token)))
    
    # check connection
    if (res$status_code != '200'){
    stop(paste("Connection Failed! Please see the following detail: \n",res))
    }
    
    obj <- httr::content(res, as = "text")
    
    json_data <- jsonlite::fromJSON(obj, flatten = TRUE)
    
    # ouputs the screen_name and followers count as a data frame.
    screen_name <- as.data.frame(json_data$screen_name)
    followers_count <- as.data.frame(json_data$followers_count)
    data <- merge(screen_name, followers_count)
    colnames(data) <- c('screen_name', 'followers_count')
    

    return(data)
    
}