Re: [Boost-users] statistics: exact median, first and third quartile

Subject: Re: [Boost-users] statistics: exact median, first and third quartile
From: James Hirschorn (James.Hirschorn_at_[hidden])
Date: 2013-03-01 10:51:25

gast128 wrote:

> Steven Watanabe <watanabesj <at> gmail.com> writes:

>> 
>> This is called std::nth_element.
>> 

> 
> Thx, but are you sure? Median is defined as the middle element in odd
> distributions but is the average of the 2 middle elements in even
> distributions.

So? For a collection c of size 2n, you would use:

nth_element( begin(c), begin(c) + n - 1, end(c) );
nth_element( begin(c), begin(c) + n, end(c) );
auto median = (c[n - 1] + c[n]) / 2;

> For quartiles (or generalized quantiles) its even worse:
> there are multiple definitions for quartiles. I even had an article listed
> 11 definitions of calculating the quartile:
> http://www.amstat.org/publications/jse/v14n3/langford.html. Still it would
> have been better if Boost had done the thinking for me :)

Definitely!