- | Pair two samples. It's like 'G.zip' but requires that both
--   samples have equal size.
pair :: (G.Vector v a, G.Vector v b, G.Vector v (a,b)) => v a -> v b -> v (a,b)
pair va vb
  | G.length va == G.length vb = G.zip va vb
  | otherwise = error "Statistics.Sample.pair: vector must have same length"

pair :: (G.Vector v a, G.Vector v b, G.Vector v (a,b)) => v a -> v b -> v (a,b)
pair va vb
  | G.length va == G.length vb = G.zip va vb
  | otherwise = error "Statistics.Sample.pair: vector must have same length"
pair va vb
  | G.length va == G.length vb = G.zip va vb
  | otherwise = error "Statistics.Sample.pair: vector must have same length"