初学者。我尝试从数据框中删除值，列或行时收到错误。实施例...
## vectors
Died.At <- c(22,40,72,41)
Writer.At <- c(16, 18, 36, 36)
First.Name <- c("John", "Edgar", "Walt", "Jane")
Second.Name <- c("Doe", "Poe", "Whitman", "Austen")
Sex <- c("MALE", "MALE", "MALE", "FEMALE")
Date.Of.Death <- c("2015-05-10", "1849-10-07", "1892-03-26","1817-07-18")
## data frame
writers_df <- data.frame(Died.At, Writer.At, First.Name, Second.Name, Sex, Date.Of.Death)
#remove value
writers_df [1,3] <- NULL
我收到错误：[<-.factor中的错误（*tmp*，iseq，value = NULL）：
替换的长度为零
另外：警告信息：
在is.na（value）中：is.na（）应用于类型＆＃39; NULL＆＃39;