library(tidytext)
dtm <- cast_dtm(doc_term_count, no, presidenttw, words, n)

Classes ‘tbl_df’, ‘tbl’ and 'data.frame':   1054900 obs. of  4 variables:
$ no         : int  1 1 1 1 1 1 1 1 1 1 ...
$ presidenttw: chr  "Chen" "Chen" "Chen" "Chen" ...
$ words      : chr  "" "一日" "一再" "一延" ...
$ n          : int  1 2 2 1 1 2 1 1 1 1 ...