Counting the number of elements with the values of x in a vector

Question

I have a vector of numbers:

numbers <- c(4,23,4,23,5,43,54,56,657,67,67,435,          453,435,324,34,456,56,567,65,34,435) 

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

Answer 1

You can just use table():

> a <- table(numbers) > a numbers   4   5  23  34  43  54  56  65  67 324 435 453 456 567 657    2   1   2   2   1   1   2   1   2   1   3   1   1   1   1  

Then you can subset it:

> a[names(a)==435] 435    3 

Or convert it into a data.frame if you're more comfortable working with that:

> as.data.frame(table(numbers))    numbers Freq 1        4    2 2        5    1 3       23    2 4       34    2 ... 

Answer 2

The most direct way is sum(numbers == x).

numbers == x creates a logical vector which is TRUE at every location that x occurs, and when suming, the logical vector is coerced to numeric which converts TRUE to 1 and FALSE to 0.

However, note that for floating point numbers it's better to use something like: sum(abs(numbers - x) < 1e-6).