subsample: Subsample from a list of data matrix
In pengminshi/cFIT: cFIT (common Factor Space Integration & Transfer)

Subsample the samples in each batch, eighter weighted with the input weight.list or unweighted.

1	subsample(X.list, subsample.prop, min.samples = 20, weight.list = NULL)

`X.list`	a list of m ncells-by-ngenes, gene expression matrices from m data sets
`subsample.prop`	a scalar between 0 and 1. smaller proportion with results in fast computation but less accurate results.
`min.samples`	integer, minimum number of samples from each batch (20 by default).
`weight.list`	weights for performing weighted subsampling sketching. Note that the weight.list is a list of weights per batch. The weights for each batch is a vector of nonnegative values of the same size as the number of cells in the batch. No weight by default (weight.list=NULL).