How Does the `Prop. Table()` Function Work in R?
I've Just Started Learning R and Have Had Trouble Finding an (Understandable) Explanation of What the Prop. Table() Function Does. I Found the Following...
I've just started learning r and have had trouble finding an (understandable) explanation of what the prop.table() function does. I found the following explanation and example:
prop.table: Express Table Entries as Fraction of Marginal Table
Examples
m <- matrix(1:4, 2) m prop.table(m, 1)
But, as a beginner, I do not understand what this explanation means. I've also attempted to discern its functionality from the result of the above example, but I haven't been able to make sense of it.
With reference to the example above, what does the prop.table() function do? Furthermore, what is a "marginal table"?
3 Answers
The values in each cell divided by the sum of the 4 cells:
prop.table(m)
The value of each cell divided by the sum of the row cells:
prop.table(m, 1)
The value of each cell divided by the sum of the column cells:
prop.table(m, 2)
I think this can help
include all those things like prop.table(m), prop.table(m, 1), prop.table(m, 2)
m <- matrix(1:4, 2)
> m
[,1] [,2]
[1,] 1 3
[2,] 2 4
> prop.table(m) #sum=1+2+3+4=10, 1/10=0.1, 2/10=0.2, 3/10=0.3,4/10=0.4
[,1] [,2]
[1,] 0.1 0.3
[2,] 0.2 0.4
> prop.table(m,1)
[,1] [,2]
[1,] 0.2500000 0.7500000 #row1: sum=1+3=4, m(0,0)=1/4=0.25, m(0,1)=3/4=0.75
[2,] 0.3333333 0.6666667 #row2: sum=2+4=6, m(1,0)=2/6=0.33, m(1,1)=4/6=0.66
> prop.table(m,2)
[,1] [,2]
[1,] 0.3333333 0.4285714 #col1: sum=1+2=3, m(0,0)=1/3=0.33, m(1,0)=2/3=0.4285
[2,] 0.6666667 0.5714286 #col2: sum=3+4=7, m(0,1)=3/7=0.66, m(1,1)=4/7=0.57
>
when m is the 2D matrix: (m,1) refers to a fraction of row marginal table (sum over each row), (m,2) refers to a fraction of column marginal table (sum over each column). In short, just a "% of total sum of row of column", if you dont want to care about the term marginal.
Example:
m with extra row and column margin
[,1] [,2] ***
[1,] 1 4 5
[2,] 2 5 7
[3,] 3 6 9
*** 6 15
> prop.table(m,1)
` [,1] [,2]
[1,] 0.2000000 0.8000000
[2,] 0.2857143 0.7142857
[3,] 0.3333333 0.6666667
> prop.table(m,2)
[,1] [,2]
[1,] 0.1666667 0.2666667
[2,] 0.3333333 0.3333333
[3,] 0.5000000 0.4000000
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