R语言download.file函数无法下载文件

download.file(url = "http://dapengde.com/r4rookies/us.csv",destfile = 'c:/r4r/us.csv')
trying URL 'http://dapengde.com/r4rookies/us.csv'
Error in download.file(url = "http://dapengde.com/r4rookies/us.csv", destfile = "c:/r4r/us.csv") : 
  cannot open URL 'http://dapengde.com/r4rookies/us.csv'
In addition: Warning message:
In download.file(url = "http://dapengde.com/r4rookies/us.csv", destfile = "c:/r4r/us.csv") :
  URL 'http://dapengde.com/r4rookies/us.csv': status was 'Couldn't connect to server'

代码中网址写错了，漏写了www，写成如下即可：

download.file(url = "http://www.dapengde.com/r4rookies/us.csv",destfile = 'us.csv')

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