[R] number to volume weighted distribution

Thierry Onkelinx thierry.onkelinx at inbo.be
Fri Nov 24 22:02:12 CET 2017

Hi Petr,

I think that Duncan suggests something like this:

x<- c(rep(10,20), rep(300,5), rep(100, 10))
tx <- table(x)

prop.x <- tx / sum(tx)
vx <- as.integer(names(tx))
prop.wx <- tx * vx / sum(tx * vx)

plot(vx, cumsum(prop.x), ylim = 0:1)
plot(vx, cumsum(prop.wx), ylim = 0:1)

Best regards,


ir. Thierry Onkelinx
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2017-11-24 14:30 GMT+01:00 PIKAL Petr <petr.pikal op precheza.cz>:
> Hi Duncan
> I tried Ecdf and/or wtd.quantile from Hmisc and it is working (probably).
> Ecdf(x, q=.5)
> Ecdf(x, weights=xw,col=2, add=T, q=.5)
> wtd.quantile(x)
>   0%  25%  50%  75% 100%
>   10   10   10  100  300
> wtd.quantile(x, weights=xw, type="i/n")
>       0%      25%      50%      75%     100%
>  10.0000 138.8667 192.5778 246.2889 300.0000
> But could you please be more specific in this?
>> But you seem to be asking about a
>> definition rather than a function:  it is obtained simply by normalizing the
>> weights to sum to 1, then evaluating cumulative sums of them.
> Actually, when I correctly calculate weights
> xw <- (x^3)/sum(x^3)
> sum(xw) equals to 1
> but how can I plot ecdf with volume weighted data. Obviously
> ecdf(x*xw) or ecdf(x^3*xw) is not correct.
> Cheers
> Petr
>> -----Original Message-----
>> From: Duncan Murdoch [mailto:murdoch.duncan op gmail.com]
>> Sent: Friday, November 24, 2017 12:36 PM
>> To: PIKAL Petr <petr.pikal op precheza.cz>; r-help op r-project.org
>> Subject: Re: [R] number to volume weighted distribution
>> On 24/11/2017 6:27 AM, PIKAL Petr wrote:
>> > Dear all
>> >
>> > Strictly speaking it is not R question but as you are the most capable persons I
>> know I give it a try.
>> >
>> > I am strugling with recalculation of number weighted to volume weighted
>> distribution.
>> >
>> > Suppose I have objects (cubes) with size
>> >
>> > x<- c(rep(10,20), rep(100, 10), rep(300,5)) I can get
>> >
>> > plot(ecdf(x))
>> >
>> > or the number weighted average
>> >
>> > mean(x)
>> > [1] 77.14286
>> >
>> > or volume weighted average
>> > weighted.mean(x, (x/sum(x^3)))
>> > [1] 204.4444
>> >
>> > However I am struggling with volume weighted ecdf.
>> >
>> > Can you please give me some hints?
>> I believe base R doesn't have a function for this, but Google says it exists in a
>> couple of packages:  spatstat, Hmisc.  But you seem to be asking about a
>> definition rather than a function:  it is obtained simply by normalizing the
>> weights to sum to 1, then evaluating cumulative sums of them.
>> Duncan Murdoch
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