How does the `prop.table()` function work in r?

user_6828329 0
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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"?

r
3 Answers

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
>
user_64201600

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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