Mining Massive Datasets - Map Reduce 6a

mmds-q6a.R

# mmds Week6A
# Q1
# Using the matrix-vector multiplication described in Section 2.3.1, applied to the matrix and vector:
# 1	2	3	4
# 5	6	7	8
# 9	10	11	12
# 13	14	15	16
#
# 1
# 2
# 3
# 4
# apply the Map function to this matrix and vector. Then, identify in the list below, one of the key-value pairs that are output of Map.
#
x <- matrix(c(1, 5, 9, 13, 2,6,10,14,3,7,11,15,4,8,12,16), nrow=4, ncol=4)
y <- matrix(1:4, nrow=4, ncol=1)

# Multiply matrix by vector.
reduce <- sweep(x, MARGIN=2, y, '*')

# List map/reduce pairs.
row <- 1
count <- 0
pairs <- sapply(seq_along(reduce), function(index) {
  if (count == 4) {
    count <<- 0
    row <<- row + 1
  }
  
  count <<- count + 1
  
  list(c(row, t(reduce)[index]))
})

pairs