Count sublists which match pattern

Question

I have a list which looks like this: data={{12,0},{0,0},{20,1},{0,0}, {0,-1}}. Now I would like to count the number of sublists which:

• have both slots zero
• the first slot zero and the second not
• the second slot zero and the first not
• the first slot < 10 and any the second zero

Answer 1

Using Cases and Count:

{Count[data, {0, 0}], Count[data, {0, _}], 
  Count[data, {_, 0}], 
  Count[data, {0, Except[0]}], 
  Count[data, {Except[0], 0}], 
  Count[data, {a_, 0} /; a < 10]}
  (* {2, 3, 3, 1, 1, 2} *)

 {Cases[data, {0, 0}], 
  Cases[data, {0, _}], 
  Cases[data, {_, 0}], 
  Cases[data, {0, Except[0]}], 
  Cases[data, {Except[0], 0}], 
  Cases[data, {a_, 0} /; a < 10]}
 (* {{{0, 0}, {0, 0}}, 
    {{0, 0}, {0, 0}, {0, -1}}, 
    {{12, 0}, {0, 0}, {0,  0}}, 
    {{0, -1}}, 
    {{12, 0}}, 
    {{0, 0}, {0, 0}}}*)