Method for indexing [] of objects of class power_array. The method makes sure that the resulting array is of class power_array and keeps and updates the object's attributes. These attributes are needed for various functions in the powergrid package to work well. ##' The indexing functions as normal indexing, but note that drop is FALSE by default, so that the resulting array has the same dimensions as the original array. The number of levels at each dimension may be reduced, however. ##'
See also
PowerGrid
ArraySlicer for a different method of reducing the
dimensions of an array of class power_array.
Examples
## Define grid of assumptions to study:
sse_pars = list(
n = seq(from = 10, to = 50, by = 20), # sample size
delta = seq(from = 0.5, to = 1.5, by = 0.5), # effect size
sd = seq(.1, 1, .3)) # standard deviation
## Define function that calculates power based on these assumptions:
PowFun <- function(n, delta, sd){
ptt = power.t.test(n = n/2, delta = delta, sd = sd,
sig.level = 0.05)
return(ptt$power)
}
## Evaluate at each combination of assumptions:
powarr = PowerGrid(pars = sse_pars, fun = PowFun, n_iter = NA)
powarr[2, 1, ] # gives the same as
#> [1] 1.0000000 0.9104815 0.4716852 0.2619313
#> Array of class `power_array` created using
#> PowerGrid.
#> One resulting dimension (dimension's name was dropped by indexing).
#>
powarr['30', '0.5', ]
#> [1] 1.0000000 0.9104815 0.4716852 0.2619313
#> Array of class `power_array` created using
#> PowerGrid.
#> One resulting dimension (dimension's name was dropped by indexing).
#>