Question

I have a matrix and an array:

m = Matrix[
 [1, 2, 3],
 [11, 15, 20]
]

array = [11, 13, 14, 18]

Is there a way to determine which elements from the array lie between the top and bottom rows of each column of the matrix? Thanks.

Answer 1

It’s not perfectly clear what you mean by “between”, but a simple understanding is:

def filter_array_between_first_and_last_rows_of_matrix(array,m)
  lower = m.row_vectors.first.max
  upper = m.row_vectors.last.min
  array.select{|e| lower < e && e < upper}
end

here’s another interpretation:

def filter_array_between_first_and_last_rows_of_matrix(array,m)
  bounds_pairs = m.column_vectors.map { |cv| [cv.first, cv[-1]] }
  array.select {|e| bounds_pairs.any? { |lo,hi| lo < e && e < hi } }
end