library(lubridate)
library(tidyverse)

dt <- readxl::read_excel('reviewsNINA.xlsx')
dt <- dt %>% mutate(date = ymd(date), roundDat= round_date(date,'month'))

Total reviews:

nrow(dt)

## [1] 4490

ggplot(data = dt, aes(x = round_date(date, '4 months'), y = rating)) + 
  stat_summary(fun.y="mean", geom="line") +
  ylim(0,5) +
  ggtitle("NINA: Mean score (4-months)") +
  scale_x_date(name = 'date', date_labels = '%b %y', breaks = '8 month')

ggplot(data = dt) +
  geom_histogram(aes(x = date), bins = 120) +
  scale_x_date(date_labels = '%b %y', breaks = '8 month') +
  theme(axis.text.x = element_text(angle = 45, hjust = 1)) +
  ggtitle('Number of reviews by date')

We can also extract the review for people who reviewed more than once

dt_double <- dt %>% count(names) %>% arrange(desc(n)) %>% filter(between(n , 2, 5)) %>% left_join(dt, by = 'names')
dt_double

## # A tibble: 57 x 7
##    names       n date       review           helpfulVotes rating roundDat  
##    <chr>   <int> <date>     <chr>            <chr>         <dbl> <date>    
##  1 Boris …     3 2019-02-10 Bitte bringt di… 2                 2 2019-02-01
##  2 Boris …     3 2018-09-06 Rückmeldung aus… 0                 1 2018-09-01
##  3 Boris …     3 2017-07-14 Ahhh. Endlich i… 1                 5 2017-07-01
##  4 Hans D…     3 2016-08-16 Funktioniert ta… 0                 5 2016-08-01
##  5 Hans D…     3 2016-07-23 Katwarn ist das… 0                 1 2016-08-01
##  6 Hans D…     3 2015-07-30 Gute und wichti… 0                 4 2015-08-01
##  7 Stefan…     3 2017-01-11 Stimmt genau     0                 5 2017-01-01
##  8 Stefan…     3 2017-01-04 Macht was sie s… 0                 5 2017-01-01
##  9 Stefan…     3 2015-08-18 Katwarn hatte s… 1                 1 2015-09-01
## 10 Andreas     2 2018-01-18 Da derzeit zum … 0                 4 2018-02-01
## # … with 47 more rows