## bootstrap on aggregated data

### 24 Aug 2015

If you have a data where ech row represents a separate observation then getting a bootstrap sample from it is just

```
sample(data, replace = TRUE)
```

If your data is aggregated so that every row represents many observations with a count column to indicate the number of observations, then the following function gives you a bootstrap sample

```
agg_bootstrap <- function(dat, cts_colname) {
cts <- dat[[cts_colname]]
# do the bootstrap sampling
idxs <- sample(seq_along(cts), prob = cts, size = sum(cts), replace = TRUE)
# aggregate results of sampling
idx_ct <- tabulate(idxs, nbins = nrow(dat))
# add bookstrap column and set values
dat[[paste0(cts_colname, "bootstrap")]] <- idx_ct
}
```