gene_expression_means_by_factors: Compute mean expression for each gene for every combination...
In AHallLab/triad.expression: Analysis of gene expresson for wheat genome triads.

Compute mean expression for each gene for every combination of factor levels.

1	gene_expression_means_by_factors(expression, metadata, factorList)

`expression`	A data frame of expression values in which each column is a sample, and each row is a single gene.
`metadata`	A data frame containing metadata for each sample.
`factorList`	A list of column names that exist in 'metadata' (as strings) to use as a factors.
`homology`	A data frame of metadata about each triad. Include which genes make them up on the A, B, and D genomes.