fixes #137 (new getMembers function)

Rfacebook/ChangeLog

@@ -82,3 +82,4 @@
     - searchGroups now returns 25+ results
 2017-07-11 - version 0.6.17
     - getUsers now works with recent versions of API
+    - getMembers function added (thanks Yan Turgeon)

Rfacebook/DESCRIPTION

@@ -4,7 +4,7 @@ Description: Provides an interface to the Facebook API.
 Version: 0.6.17
 Date: 2017-07-11
 Author: Pablo Barbera <[email protected]>, Michael Piccirilli
-    <[email protected]>, Andrew Geisler, Wouter van Atteveldt
+    <[email protected]>, Andrew Geisler, Wouter van Atteveldt, Yan Turgeon
 Maintainer: Pablo Barbera <[email protected]>
 URL: https://github.com/pablobarbera/Rfacebook
 BugReports: https://github.com/pablobarbera/Rfacebook/issues

Rfacebook/NAMESPACE

@@ -10,6 +10,7 @@ export(getFriends)
 export(getGroup)
 export(getInsights)
 export(getLikes)
+export(getMembers)
 export(getNetwork)
 export(getNewsfeed)
 export(getPage)

Rfacebook/R/getMembers.R

@@ -0,0 +1,49 @@
+#' @rdname getMembers
+#' @export
+#' @title
+#' Retrieve members from a public group
+#'
+#' @description
+#' \code{getMembers} retrieves members from a public group, up to 5000 members.
+#'
+#' @param page A group ID
+#'
+#' @author
+#' Yan Turgeon
+#' @seealso \code{\link{getPage}}, \code{\link{getPost}}, \code{\link{getCommentReplies}}
+
+#' @param token Either a temporary access token created at
+#' \url{https://developers.facebook.com/tools/explorer} or the OAuth token 
+#' created with \code{fbOAuth}.
+#' 
+#' @examples \dontrun{
+#' ## Find Facebook ID for R-Users Facebook group
+#'	load("fb_oauth")
+#'	ids <- searchGroup(name="rusers", token=fb_oauth)
+#'  ids[1,] # id = 18533493739
+#' ## Retrieves members ID for R-Users Facebook group
+#'  members <- getMembers(group_id="18533493739", token=fb_oauth)
+#'}
+
+getMembers <- function(group_id, token, n=5000, api=NULL){
+    url <- paste0('https://graph.facebook.com/', group_id,
+                  '/members?fields=id,name,first_name,last_name,administrator&limit=', n)
+
+    # making query
+  content <- callAPI(url=url, token=token)
+
+ #if no data, return error message
+  if (length(content$data)==0){ 
+    message("No groups with this name were found.")
+    return(data.frame())
+  }
+
+  # if data, return a data frame
+  df <- data.frame(
+    name = unlist(lapply(content$data, '[[', 'name')),
+    id = unlist(lapply(content$data, '[[', 'id')),
+    administrator = unlist(lapply(content$data, '[[', 'administrator')),
+    stringsAsFactors=F)
+
+  return(df)
+}