counting things

Sometimes things that are really easy to do in excel are not so intuitive in R. Like counting things. Because most of the time I am working with data in long format, you can end up with hundreds of observations, so functions like length() aren’t useful. Today I just wanted to check how many participants were in this dataset and it took me some significant googling.

load packages
create a little df
df <- data.frame("pp_no" = 1:16, 
                "delay" = c("short","long"), "condition" = c("easy", "easy", "difficult", "difficult"),
                "score" = c(82, 75, 76, 72, 86, 89, 85, 87, 87, 76, 78, 85, 97, 87, 94, 87))

count distinct values

My intuition is to use the distinct() function from dplyr, but it SELECTS distinct rows, but doesn’t count them.

It is the n_distinct() function will give you a count of the distinct values in a variable

## [1] 16

counting by levels

The other counting thing I do a lot if count by group (or other categorical variable). Although there is a few lines of code, combining group_by() and summarise() is useful because you create a df that can combines both the count and other summary stats.

option 1: group_by x summarise

df %>%
  group_by(delay) %>%
  summarise(count = n(), mean_score = mean(score))
## # A tibble: 2 x 3
##   delay count mean_score
##   <fct> <int>      <dbl>
## 1 long      8       82.2
## 2 short     8       85.6

option 2: table()

If you just want a fast count, table() by categorical variable will count observations by condition

##  long short 
##     8     8

option 3: janitor::tabyl

When things are less evenly distributed janitor::tabyl() is useful because it gives % as well as n

##  df$delay n percent
##      long 8     0.5
##     short 8     0.5