I have a vector of numbers:
v1 <- c(1,2,3)
and I want to programmatically analyze the impact of sign change whose variants could be:
v1[1] + v1[2] + v1[3]
[1] 6
v1[1] + v1[2] - v1[3]
[1] 0
v1[1] - v1[2] - v1[3]
[1] -4
v1[1] - v1[2] + v1[3]
[1] 2
How can I exchange signs ('+', '-') programatically? I'm thinking this is a silly question, but can't think my way out of my box, though my line of analysis points to evaluating changing signs.
Here's a quick way to get all possibilities with matrix multiplication:
signs = rep(list(c(1, -1)), length(v1))
signs = do.call(expand.grid, args = signs)
signs$sum = as.matrix(signs) %*% v1
signs
# Var1 Var2 Var3 sum
# 1 1 1 1 6
# 2 -1 1 1 4
# 3 1 -1 1 2
# 4 -1 -1 1 0
# 5 1 1 -1 0
# 6 -1 1 -1 -2
# 7 1 -1 -1 -4
# 8 -1 -1 -1 -6
If you don't want all combinations, you could filter down the signs data frame to the combos of interest, or build it in a way that only creates the combos you care about.