How to access values ​​in a frequency table

Question

I have a frequency table that counts the frequency of elements in a vector

a = table(c(0,1,1,1,0,2,2,4,1,2,3,2,1,2,3,1,1,1,2,3,4,1,1,0)) a # 0 1 2 3 4 # 3 10 6 3 2 

I know that I can get the name by name (s). But when I tried to access the SECOND values ​​of the string

 a[1, "0"] # Error in a[1, "0"] : incorrect number of dimensions a[1, 1] # Error in a[1, 1] : incorrect number of dimensions 

Answer 1

This table is actually an array.

 x <- c(0,1,1,1,0,2,2,4,1,2,3,2,1,2,3,1,1,1,2,3,4,1,1,0) (a <- table(x)) # # 0 1 2 3 4 # 3 10 6 3 2 class(unclass(a)) # [1] "array" 

His names are on top, and the meanings below.

 names(a) [1] "0" "1" "2" "3" "4" 

You can access your items in several ways.

 a[1] ## access named element by index # 0 # 3 a[[1]] ## access unnamed element by index # [1] 3 a["0"] ## access named element by name # 0 # 3 a[["0"]] ## access unnamed element by name # [1] 3 as.vector(a) ## as.vector() drops table down to unnamed vector # [1] 3 10 6 3 2 c(a)[2:4] ## c() drops table down to named vector # 1 2 3 # 10 6 3 class(a[2:4]) # [1] "array" class(c(a)[2:4]) # [1] "integer" 

It also has the nrow and dim attribute, which is configured on the last few lines of table .

 y <- array(tabulate(bin, pd), dims, dimnames = dn) class(y) <- "table" 

Although I really do not understand why nrow(a) is 5, but a[1,] returns an error.

Answer 2

The table() command returns a named vector, not a matrix or data.frame. If you want to access the number of zeros, you would do

 a["0"] 

Please note that the numeric properties of the levels are lost, because the names of the named vectors must be characters. You can convert them using as.numeric(names(a)) if you like

Answer 3

The table you use is a one-dimensional array, and you use 2 dimensions to retrieve the element that you get this error.

Use something like [1]

Answer 4

a = as.numeric (names (a))

he will give you access to the first column