surf algorithm for multyple images

Hi everybody...when apply surf algorithm for many images ...the features for each images not same ...for example the the number of featres of first image=1000 and the second image =3000...and so on... i want to insert the features in on one fector to enter this to neural network... i used this code ..is correct to used this code:

    rr=f1(1:10 );

is this code to Determines the numbers of features and make the number of features =10 or must to used algorithm to redused the number of features???

this my code