如何根据其他列在列中提供值

Question

我的df如下

V1| V2| V3| V4
--+---+---+---
10| 1 | 3 | 2
2 | 1 | 1 | 0
0 | 3 | 0 | 2
2 | 0 | 1 | 1
0 | 0 | 2 | 3
2 | 2 | 0 | 4

我想写一个程序，所以 if（V1！= 0）则V2，v3，v4全部为0 类似地，如果V1 == 0且V2！= 0则V3，V4为零，依此类推。

我正在尝试for循环和if语句，但没有得到任何地方。有人可以帮忙吗

预期结果

V1| V2| V3| V4
--+---+---+---
10| 0 | 0 | 0 
2 |0  | 0 | 0
0 | 3 | 0 | 0 
2 | 0 | 0 | 0 
0 | 0 | 2 | 0 
2 | 0 | 0 | 0 

Answer 1

我期待用max.col在一个班轮中解决这个问题，但我无法找到方法。所以这是一个冗长的过程。

#For each row find out its 1st value which is greater than zero
indx <- max.col(df > 0, ties.method = "first")

#Convert the dataframe to matrix
mat <- as.matrix(t(df))

#Get the indices which we need to convert to zero
indices <- setdiff(1:(nrow(df) * ncol(df)), rep(ncol(df), length(indx)) * 
                                            (seq_along(indx) - 1) + indx)

#The output of rep(ncol(df), length(indx)) * (seq_along(indx) - 1) + indx is 
#[1]  1  5 10 13 19 21 
#which are the indices which we don't want to change to zero.

# Convert those indices to zero
mat[indices] <- 0
data.frame(t(mat))


#  V1 V2 V3 V4
#  10  0  0  0
#   2  0  0  0
#   0  3  0  0
#   2  0  0  0
#   0  0  2  0
#   2  0  0  0