[R] What is this called? lapply(datum,[[,ColumnName)

Hello R users I recently learned how to use this command: lapply(datum,[[,ColumnName) Unfortunately, I don't know how exactly it works, what it's called (in particular the [[ part], and what other things you can do with it (retrieve multiple columns?). Given datum is a list of

[R] Storing whole regression results

Hello seasons R users, Is it possible to store a complete regression result into an array? I've already been able to save individual regression coefficients, but would like to store the whole regression results into different arrays through a loop. So that in under different quantiles

[R] Quantile regression: Discrepencies Between optimizer and rq()

think my optimizer code is wrong and suspects it has something to do with the starting values. The results seems very sensitive to different starting values and I don't know how to make sense of it. Advice from the community would be greatly appreciated. Sincerely, Kevin Chang