Mgiyuk

Make matrix from two columns of a dataframe and populate it by third without nested for loop Let's say I have a dataframe with three of its columns being > df A B C 1232 27.3 0.42 1232 27.3 0.36 1232 13.1 0.15 7564 13.1 0.09 7564 13.1 0.63 The required output is: [1232] [7564] [13.1] 0.15 0.36 [27.3] 0.39 0 I need to make a matrix with unique values in A and B as my rows and columns. The value for any cell in the matrix is to be calculated by subsetting the original dataframe for the particular value of A and B and calculating the mean of column C. My code is: mat <- matrix(rep(0), length(unique(df$A)), nrow = length(sort(unique(df$B)))) # sort is to avoid NA colnames(mat) <- unique(df$A) rownames(mat) <- unique(df$B) for (row in rownames(mat)) { for (col in colnames(mat)) { x <- subset(df, A == col & B == row) mat[row, col] = mean(df$C) } } This is very slow, considering I have to ...