search for: x_string1

Dear R users, I have a big text file formatted like this: x x_string y y_string id1 id1_string id2 id2_string z z_string w w_string stuff stuff stuff stuff stuff stuff stuff stuff stuff // x x_string1 y y_string1 z z_string1 w w_string1 stuff stuff stuff stuff stuff stuff stuff stuff stuff // x x_string2 y y_string2 id1 id1_string1 id2 id2_string1 z z_string2 w w_string2 stuff stuff stuff stuff stuff stuff stuff stuff stuff // ... ... I'...