Download or view average.frink in plain text format
/** This function contains methods for finding the averages (mean and mode(s))
along with the standard deviation of an enumerating expression of data.
This is now part of Frink's standard library and this file does not need to
be included.
These use Welford's algorithm for calculating the "Corrected Sum of Squares"
which are the "sum of squares of the deviations of the values about their
mean."
Welford, B. P. (1962). Note on a Method for Calculating Corrected Sums of
Squares and Products. Technometrics, 4(3), 419–420.
doi:10.1080/00401706.1962.10490022
https://sci-hub.se/https://doi.org/10.1080/00401706.1962.10490022
*/
/** Calculates the mean and standard deviation of an array or
enumerating expression.
This uses Welford's algorithm as cited in Knuth, The Art of Computer
Programming, Vol. 2, 3rd edition, page 232.
This gets the units of measurement right and can even be used symbolically.
Arguments:
[list, sample]
where
list: is an array or enumerating expression of the items to average.
sample: a boolean flag indicating if we want the standard deviation to be
the sample standard deviation (=true) or the population standard
deviation (=false). If you are in doubt, it's probably safer and
more conservative to set this to true (for sample standard
deviation) giving a larger standard deviation.
Returns:
[mean, sd, number]
where
mean is the mean of the sequence of data
sd is the (population or sample) standard deviation
number is the number of elements in the list.
*/
meanAndSD[list, sample] :=
{
M = undef // Make units come out right
S = undef
k = 1
for v = list
{
if M == undef
{
M = v
S = 0 v^2 // Make units come out right
} else
{
oldM = M
diff = v - oldM
M = M + diff / k
S = S + diff * (v - M)
}
k = k+1
}
if sample == true
sub = 1 // Sample standard deviation, subtract 1 from num
else
sub = 0 // Population standard deviation
return [M, sqrt[S/(k-1-sub)], k-1]
}
/** Calculates the mean of an array or enumerating expression.
This uses Welford's algorithm as cited in Knuth, The Art of Computer
Programming, Vol. 2, 3rd edition, page 232.
This gets the units of measurement right and can even be used symbolically.
Arguments:
[list]
where
list: is an array or enumerating expression of the items to average.
Returns:
the mean of the list.
*/
mean[list] :=
{
M = undef // Make units come out right
k = 1
for v = list
{
if M == undef
M = v // Make units come out right.
else
M = M + (v - M) / k
k = k+1
}
return M
}
/** Returns the mode(s) of a list, that is, the value(s) that occur the most
times. Each element of the list must be a hashing expression, that is, can
be used as a key in a dictionary.
This always returns an array because there are potentially multiple
equivalent modes in a distribution. This uses the more general
mostCommon[list] function to do the work. The modes are not returned in
any specific order (because they might actually be non-comparable to each
other.)
For example,
modes[[1, 1, 1, 2, 4, 4, 4]]
returns
[1, 4]
because 1 and 4 both occur the same number of times.
*/
modes[list] :=
{
return mostCommon[list]@0
}
Download or view average.frink in plain text format
This is a program written in the programming language Frink.
For more information, view the Frink
Documentation or see More Sample Frink Programs.
Alan Eliasen was born 20217 days, 23 hours, 27 minutes ago.