Asking for help with bootstrap. Please!!

Hi

im trying to do a bootstrap, the problem is:

i have 2 columns

Age Length
1 140
1 142
1 146
1 149
2 156
2 157
3 168
4 190

Thats an example, now when i make the bootstrao its very important to not mix the datas. i cant get an age 1 with a length of 190.


i hope u can help.


Thanks, Marcelino.