The function will take an object of class 'spdesign' and add a blocking column to the design matrix. The function will use random permutations of the blocking column to find the column that minimizes correlation between the blocking column and the design columns. Specifically the target for the minimization procedure is the mean squared correlation.
block(x, blocks, target = 5e-04, max_iter = 1e+06)
An object of class 'spdesign'
An integer giving the number of blocks. The number of blocks must be a multiple of the number of rows to ensure equal number of choices within a block.
A target value for the mean squared correlation. The default value is 0.0005. Setting the target to 0 forces the function to search all `max_iter` blocking candidates
The maximum number of candidates to consider before returning the best blocking candidate. The default value is 1000000.
A modified 'spdesign' object where the design is replaced with the same design and a blocking column. In addition a correlation vector, number of iterations and the target value are returned as part of the modified 'spdesign' object.
The function uses a random permutation so every time you run the function you will get a slightly different blocking column. You can set a seed prior to calling the function to always return the same blocking vector.
If you pass in a design that already contains a blocking column, then this blocking column will be replaced without warning.