Hi List. I've to perform a sequence of conditional sampling without repetition from a very simple data frame. It contains the samples and people names (which picked the sample). Something like this (but much more longer): Sample Picker 4ME1B2 B Ana 4ME1C1 B Ana 4ME1D2 C Ana 4ME1E2 C Ana 4ME1E3 A Ana 4ME2A1 C Ana 4ME2D2 B Ana 4CME3 B Ingrid 4CME7 C Ana 4ME1B1 C Elis 4ME1B2 C Elis 4ME1C1 C Elis 4ME1D2 A Elis 4ME2B2 B Elis 4ME2B3 A Ingrid 4ME2B4 A Elis 4ME2C1 B Elis 4ME2C4 C Elis 4ME2D3 C Ingrid 4ME2C2 C Ingrid 4ME2D1 B Ingrid 4ME2D2 C Ingrid Well then, these samples must be reviewed. To do so I've to create random sets of samples for each person that not include the person's own samples and, obviously, can't repeat samples at the next set (of the next person). Each person will have to review the same number of samples he/she picked. I've tried sample() function, but it doesn't do well with data frames, so it's getting tricky to work around. Any suggestions or ideas? Thank you for your attention and sorry for the silly question. ------------------------------------------------------------------- MSc. <mailto:r.aluizio@gmail.com> Rodrigo Aluizio [[alternative HTML version deleted]]