freq.array {boot}  R Documentation 
Take a matrix of indices for nonparametric bootstrap resamples and return the frequencies of the original observations in each resample.
freq.array(i.array)
i.array 
This will be an matrix of integers between 1 and n, where n is the number
of observations in a data set. The matrix will have n columns and R rows
where R is the number of bootstrap resamples. Such matrices are found by

A matrix of the same dimensions as the input matrix. Each row of the matrix corresponds to a single bootstrap resample. Each column of the matrix corresponds to one of the original observations and specifies its frequency in each bootstrap resample. Thus the first column tells us how often the first observation appeared in each bootstrap resample. Such frequency arrays are often useful for diagnostic purposes such as the jackknifeafterbootstrap plot. They are also necessary for the regression estimates of empirical influence values and for finding importance sampling weights.