read_df_block: read data frame block from file
In bigReg: Generalized Linear Models (GLM) for Large Data Sets

read data frame block from file

1	read_df_block(size, filePath, df, ncol, factors, factor_indices)

`size`	number of elements in the block
`filePath`	path to where the block is stored
`df`	an empty list having the same number of elements as columns in the table
`ncol`	number of columns in the dataframe block
`factors`	list containing factors
`factor_indices`	numeric vector containing the indicies that denote the factors