data.table在每行[R]中按na的數量向右移動所有單元格值

Question

如何將數據表中的單元格向右移動R中每行的NA數量？

示例數據：

data <- data.table(c1=c("a","e","h","j"),
                   c2=c("b","f","i",NA),
                   c3=c("c","g",NA,NA),
                   c4=c("d",NA,NA,NA), stringsAsFactors = F)
  c1   c2   c3   c4
1  a    b    c    d
2  e    f    g <NA>
3  h    i <NA> <NA>
4  j <NA> <NA> <NA>

示例中的所需數據：

data.desired <- data.table(
                  c1=c("a",NA,NA,NA),
                   c2=c("b","e",NA,NA),
                   c3=c("c","f","h",NA),
                   c4=c("d","g","i","j"), stringsAsFactors = F)
    c1   c2   c3 c4
1    a    b    c  d
2 <NA>    e    f  g
3 <NA> <NA>    h  i
4 <NA> <NA> <NA>  j

Answer 1

這是使用矩陣索引和按行對NA值進行計數的一種嘗試：

#convert back to a data.frame to take advantage of matrix indexing
setDF(data)   

arr <- which(!is.na(data), arr.ind=TRUE)
arr[,"col"] <- arr[,"col"] + rowSums(is.na(data))[arr[,"row"]]
out <- data
out[] <- NA
out[arr] <- data[!is.na(data)]

out
#    c1   c2   c3 c4
#1    a    b    c  d
#2 <NA>    e    f  g
#3 <NA> <NA>    h  i
#4 <NA> <NA> <NA>  j

#convert to data.table if necessary
setDT(out)

此選項非常快捷，只需短暫的測試，即可在3-4秒內遍歷4列/ 2百萬行。

Answer 2

我們可以用

data.table(t(apply(data, 1, function(x){ c(rep(NA, sum(is.na(x))), x[!is.na(x)])})))
#      V1   V2   V3 V4
# 1:    a    b    c  d
# 2: <NA>    e    f  g
# 3: <NA> <NA>    h  i
# 4: <NA> <NA> <NA>  j