text                 class.negative        class.positive       class.trust
<fctr>                    <dbl>              <dbl>              <dbl>

firmly believe...       11                   24                   3
when i thought...       3                    3                    4
fans of david...        11                   24                   12
just watched...         3                    5                    9
i was so looking...     16                   9                    10

clean.reviews = data.frame(text = reviews,class = get_nrc_sentiment(reviews), stringsAsFactors = T)
head(clean.reviews)
clean.reviews1 = as.data.frame(clean.reviews)
head(clean.reviews1)

class (class.positive-class.negative)  text
13                                     firmly believe...
0                                      when I thought...
13                                     fans of david...
2                                      just watched...
-7                                     i was so looking...

library(dplyr)
clean.reviews %>% mutate(class = class.positive - class.negative)