How to count the number of elements with the values in a vector

Question

Consider a vector of numbers:

num <- c(2,13,7,13,51,43,44,76,647,37,367,435,
         443,425,314,31,416,16,367,65,44,425)

How can I count the number of times a value 'x' appears in the vector with R?

Answer 1

You have various options to count the number of times a number occurs:

One of them is to use table():

z <- table(num)
> z
num
  2  7  13  16  31  37  43  44  51  65  76  314  367  416  425  435  443  647 
  1   1   2   1   1   1   1   2  1  1  1
1   2   1   1   1   1   1   1

Then you can subset it, for the number you want the count for:

z[names(z)==367]
367 
  2

The second option is to convert it into a data.frame

as.data.frame(table(num))
       num Freq
1        2    1
2        7    1
3       13    2
4       16    1
...

Answer 2

Use dplyr function group_by().

> n = as.data.frame(num)
> n %>% group_by(num) %>% count()

     num     n
   <dbl> <int>
 1     2     1
 2     7     1
 3    13     2
 4    16     1
 5    31     1
 6    37     1
 7    43     1
 8    44     2
 9    51     1
10    65     1
11    76     1
12   314     1
13   367     2
14   416     1
15   425     2
16   435     1
17   443     1
18   647     1