download data from database

library(httr)
library(pipeR)
library(xml2)
library(rvest)
library(stringr)

testurl = "https://tcga-data.nci.nih.gov/tcga/findArchives.htm"

x = POST(testurl, body = list(project = -1, center = -1, platform = -1, dataType = 29, archiveType = 2,
  fileName = "", dateStart="01/01/2016", dateEnd = "06/18/2016", ec_crd = 15, ec_p = 2), encode = "form") %>>%
  content %>>%
  xml_find_one("//table[@id='ec_table']") %>>% xml_find_all("//td[a='Download']/a") %>>%
  (.[xml_text(.) == "Download"]) %>>% lapply(xml_attr, attr = "href") %>>%
  str_extract("/tcgafiles/ftp_auth/distro_ftpusers/anonymous/[^']+") %>>%
  (str_c("https://tcga-data.nci.nih.gov", .))

sapply(x, function(y){
  download.file(y, destfile = str_extract(y, "mdanderson.org_.*gz"))
})