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Appendix C Formula Functions Reference 487
Random Functions
Random Poisson
Generates a Poisson variate based on the value of the parameter, lambda, you enter as the function
argument. Lambda is often a rate of events occurring per unit time or unit of area. Lambda is both the
mean and the variance of the Poisson distribution.
Random Gamma Poisson
Returns random numbers from the gamma Poisson distribution with parameters lambda and sigma.
Random Weibull
Returns a random number from a Weibull distribution.
Random Lognormal
Returns a Lognormal-distributed random number with location parameter mu and scale parameter
sigma.
Random GLog
Returns random numbers from the generalized logarithm distribution with parameters mu, sigma, and
lambda. When lambda is equal to zero, the function returns a lognormal(mu, sigma).
C Formula Functions Reference
Random Reset
Restarts the random number sequences with a seed you specify.
Col Shuffle
Selects a row number at random from the current data table. Each row number is selected only once.
When Col Shuffle is used as a subscript, it returns a value selected at random from the column that
serves as its argument. Each value from the original column is assigned only once as Shuffle’s result.
For example, to identify a 50% random sample without replacement, use the formula in Figure C.18.
Figure C.18 Formula Identifying 50% Random Sample
The formula in Figure C.18 selects half the values (n/2) from the column x and assigns them to the first
half of the rows in the computed column. The remaining rows of the computed column fill with
missing values.
Resample Freq
Generates a random selection with replacement frequency counts, suitable for use in bootstrapping. For
example, it supports a second Freq Column argument, enabling it to do bootstrap samples relating to a
pre-existing frequency column specified in the second argument. Resample Freq() generates 100%
resample. Resample Freq(fraction) generates fraction*nrow frequency sample, and Resample
Freq(n) generates an n*nrow frequency sample.