Kieran Healy shows how to get all but one element from a vector in R:
Sometimes we want to repeatedly do things with all but one row of a data frame, where we systematically drop each row in turn and do the thing. For example, jacknife cross-validation is a kind of very basic bootstrap technique. (It is computationally simpler than and predates the bootstrap.) Or in some areas “leave-one-out” summary statistics are often calculated as a quick robustness check. Sometimes we want to do this within groups, perhaps especially when the groups may be small.
Read on to see how, including several examples. H/T R-Bloggers.