如何在向量的所有元素上循环函数，除了一个元素，并将结果存储在数据框的单独列中

Question

I have a data frame with several columns. I want to run a function [pmax() in this case] over all columns whose name is stored in a vector except one, and store the result in new separate columns. At the end, I would also like to store the names of all new columns in a separate vector. A minimal example would be:

Name <- c("Case 1", "Case 2", "Case 3", "Case 4", "Case 5")
C1 <- c(1, 0, 1, 1, 0)
C2 <- c(0, 1, 1, 1, 0)
C3 <- c(0, 1, 0, 0, 0)
C4 <- c(1, 1, 0, 1, 0)
Data <- data.frame(Name, C1, C2, C3, C4)

var.min <- function(data, col.names){
                    new.df <- data

                    # This is how I would do it outside a function and without loop:
                    new.df$max.def.col.exc.1 <- pmax(new.df$C2, new.df$C3)
                    new.df$max.def.col.exc.2 <- pmax(new.df$C1, new.df$C3)
                    new.df$max.def.col.exc.3 <- pmax(new.df$C1, new.df$C2)
                    
                    new.columns <- c("max.def.col.exc.1", "max.def.col.exc.2", "max.def.col.exc.3")

                    return(new.df)
}

new.df <- var.min(Data,
                  col.names= c("C1", "C2", "C3"))

The result should look like:

    Name C1 C2 C3 C4 max.def.col.exc.1 max.def.col.exc.2 max.def.col.exc.3
1 Case 1  1  0  0  1                 0                 1                 1
2 Case 2  0  1  1  1                 1                 1                 1
3 Case 3  1  1  0  0                 1                 1                 1
4 Case 4  1  1  0  1                 1                 1                 1
5 Case 5  0  0  0  0                 0                 0                 0

Anyone with an idea? Many thanks in advance!

Answer 1

Here is a base R solution with combn . It gets all pairwise combinations of the column names and calls a function computing pmax .

Note that the order of the expected output columns is the same as the one output by the code below. If the columns vector is c("C1", "C2", "C3") , the order will be different.

Note also that the function is now a one-liner and accepts combinations of any number of columns, 2, 3 or more.

var.min <- function(cols, data) Reduce(pmax, data[cols])

cols <- c("C3", "C2", "C1")
combn(cols, 2, var.min, data = Data)
#     [,1] [,2] [,3]
#[1,]    0    1    1
#[2,]    1    1    1
#[3,]    1    1    1
#[4,]    1    1    1
#[5,]    0    0    0

Now it's just a matter of assigning column names and cbind ing with the input data.

tmp <- combn(cols, 2, var.min, data = Data)
colnames(tmp) <- paste0("max.def.col.exc.", seq_along(cols))
Data <- cbind(Data, tmp)
rm(tmp)    # final clean-up