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Apply a Function to a Data Frame Split by Factors
By(x, INDICES, FUN, COLUMNS, array = FALSE, ...)
Data frame
Indices (vector or list of indices, vector of column names, or formula of column names)
A function to be applied to data frame subsets of 'data'.
(Optional) subset of columns of x to work on
if TRUE an array/matrix is always returned
Additional arguments to lower-level functions
Klaus K. Holst
Simple wrapper of the 'by' function
By(datasets::CO2,~Treatment+Type,colMeans,~conc) By(datasets::CO2,~Treatment+Type,colMeans,~conc+uptake)
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