collection=mongo(collection="mycs", db="mydb")
ans<- collection$find()

df<-as.data.frame(ans)

extracting<-regmatches(df$text,gregexpr("#(\d|\w)+",df$text))

ndf<-as.data.frame(extracting)

p = ggplot(ndf, aes(x = ndf, y = freq)) + geom_bar(fill = "blue")
p

# data
df <-
  structure(list(
    created_at = c("Thu Oct 19 10:46:32 +0000 2017",
                   "Thu Oct 19 10:46:32 +0000 2017",
                   "Thu Oct 19 10:46:32 +0000 2017"),
    id = c(920964376408068096, 920964376408068096, 920964376408068096),
    text = c("RT @Nagaa27: Me on Open Science Framework  #Cryptography #kriptografi #python #freebook #ComputerScience #OpenScienc…",
             "RT @Nagaa27: Me on Open Science Framework    #Cryptography #kriptografi #python #freebook #ComputerScience #OpenScienc…",
             "RT @Nagaa27: Me on Open Science Framework  #Science #OpenScienc…")))