更改具有唯一值的多列中的值并合并为单列 (R)

Question

Let's say I have a dataset (ds) with 4 rows with 3 variables as seen below:

ds
x1  x2  x3
 1   0   0
 0   0   1
 0   1   0
 0   0   1

How do I change the "1" to a unique value for each column and combine them into a single column?

So, the first step:

x1  x2  x3
 1   0   0
 0   0   3
 0   2   0
 0   0   3

Then, the second step (creating x4 ):

x1  x2  x3  x4
 1   0   0   1
 0   0   3   3
 0   2   0   2
 0   0   3   3

I have a lot more variables than this, I just want to know how to minimize the number of lines I write so it's not like 10+ lines.

Answer 1

You could do this:

df <- read.table(text="x1  x2  x3
1   0   0
0   0   1
0   1   0
0   0   1", header=TRUE, stringsAsFactors=FALSE)

df <- df*col(df)
df$x4 <- rowSums(df)

  x1 x2 x3 x4
1  1  0  0  1
2  0  0  3  3
3  0  2  0  2
4  0  0  3  3