R help - Aug 2011 - Column of probabilities

Hi all,
I have a vector xm say:  xm = c(1,2,3,4,5,5,5,6,6)

I want to return a vector with the corresponding probabilities based on the
amount of times the numbers occurred. For example, I should get the
following vector for xm:
prob.xm = c(1/9, 1/9, 1/9, 1/9, 3/9, 3/9, 3/9, 2/9, 2/9)
Any help greatly appreciated.

-- 
Thanks,
Jim.

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Try this:

prob.xm <- (table(xm)/length(xm))[match(xm, sort(unique(xm)))]

Jean


Jim Silverton wrote on 08/24/2011 02:31:05 PM:
> Hi all,
> I have a vector xm say:  xm = c(1,2,3,4,5,5,5,6,6)
> 
> I want to return a vector with the corresponding probabilities based on 
the
> amount of times the numbers occurred. For example, I should get the
> following vector for xm:
> prob.xm = c(1/9, 1/9, 1/9, 1/9, 3/9, 3/9, 3/9, 2/9, 2/9)
> Any help greatly appreciated.
> 
> -- 
> Thanks,
> Jim.
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If your numbers are all positive integers, this should work:

(tabulate(xm)[xm])/length(xm)

it can be put into a function for ease of use:

probVec <- function(x) {(tabulate(x)[x])/length(x)}

You'll have some trouble if you have non-positive integers or non-integers.
Let me know if you need to handle that case: it's not much harder (just a
transform in and out of integers).

Hope this helps,

Michael

On Wed, Aug 24, 2011 at 3:31 PM, Jim Silverton
<jim.silverton@gmail.com>wrote:
> Hi all,
> I have a vector xm say:  xm = c(1,2,3,4,5,5,5,6,6)
>
> I want to return a vector with the corresponding probabilities based on the
> amount of times the numbers occurred. For example, I should get the
> following vector for xm:
> prob.xm = c(1/9, 1/9, 1/9, 1/9, 3/9, 3/9, 3/9, 2/9, 2/9)
> Any help greatly appreciated.
>
> --
> Thanks,
> Jim.
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

On Aug 24, 2011, at 3:31 PM, Jim Silverton wrote:
> Hi all,
> I have a vector xm say:  xm = c(1,2,3,4,5,5,5,6,6)
>
> I want to return a vector with the corresponding probabilities based  
> on the
> amount of times the numbers occurred. For example, I should get the
> following vector for xm:
> prob.xm = c(1/9, 1/9, 1/9, 1/9, 3/9, 3/9, 3/9, 2/9, 2/9)
?prop.table

Usage (with table)

 > prob.xm <- round( prop.table(table(xm)), digits=3)
 > prob.xm
xm
     1     2     3     4     5     6
0.111 0.111 0.111 0.111 0.333 0.222

-- 

David Winsemius, MD
West Hartford, CT

H all,

I have a 6 x 3 matrix. The last column is simply the sum of of the first two
rows.

x1  x2   x3
1     2    3
2     1    3
1     0    1
2     2    4
2     1    3
2     1    3
0     0    0

I want to create a column of probabilities p, such that for each row, I want
to find the probability of x1=k and x3 = n divided by the probability that
x3 = n.
So I should end up with a column of probabilities:
1/4, 3/4, 1/7, 1/7, 3/4, 3/4, 1/7


-- 
Thanks,
Jim.

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