How can I count the number of times a value occurs in a column of a dataframe?

Question

Is there a simple way of identifying the number of times a value is in a vector or column of dataframe? I essentially want the numerical values of a histogram but I do not know how to access it.

# sample vector
a <- c(1,2,1,1,1,3,1,2,3,3)

#hist
hist(a)

Thank you.

UPDATE:

On Dirk's suggestion I am using hist. Is there a better way than than specifying the range as 1.9, 2.9 etc when I know that all my values are integers?

 hist(a, breaks=c(1,1.9,2.9,3.9,4.9,5.9,6.9,7.9,8.9,9.9), plot=FALSE)$counts

Answer 1

Use table function.

Answer 2

Try this:

R> a <- c(1,2,1,1,1,3,1,2,3,3)
R> b <- hist(a, plot=FALSE)
R> str(b)
List of 7
 $ breaks     : num [1:5] 1 1.5 2 2.5 3
 $ counts     : int [1:4] 5 2 0 3
 $ intensities: num [1:4] 1 0.4 0 0.6
 $ density    : num [1:4] 1 0.4 0 0.6
 $ mids       : num [1:4] 1.25 1.75 2.25 2.75
 $ xname      : chr "a"
 $ equidist   : logi TRUE
 - attr(*, "class")= chr "histogram"
R> 

R is object-oriented and most methods give you meaningful results back. Use them.

Answer 3

If you want to use hist you don't need to specify the breaks as you did, just use the seq function

br <- seq(0.9, 9.9, 1)
num <- hist(a, br, plot=F)$counts

Also, if you're looking for a specific value you can also use which.

For instance:

num <- length(which(a == 1))