Remove rows from cell Array which have string in the first column

I have a cell array of the following format:

   M=['test'  '12'  '122' '...'
      'test2' '123' '234' []
      '1234'  'RR'  '123' []
      'test4' '123' '234' []
      '2341'  'KK'  's'   []
      '1121'  'pp'   []   []
      'tesst3' '12'  '122' '...'
  ]

I want to remove all rows that have a string which is not a number in the first column. The result array is:

   result=[   
      '1234'  'RR'  '123' []
      '2341'  'KK'  's'   []
      '1121'  'pp'   []   []

]

Answer 1

[Andrei Bobrov]

M={'test'  '12'  '122' '...'
      'test2' '123' '234' []
      '1234'  'RR'  '123' []
      'test4' '123' '234' []
      '2341'  'KK'  's'   []
      '1121'  'pp'   []   []
      'tesst3' '12'  '122' '...'}

result = M(~cellfun('isempty',regexp(M(:,1),'^\d+$')),:)

or

result = M(~isnan(str2double(M(:,1))),:)