generate column values with multiple conditions in R

Question

I have a dataframe z and I want to create the new column based on the values of two old columns of z. Following is the process:

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Answer 1

Generate a multipler vector:

tt <- rep(1, max(z$x))
tt[2] <- 2
tt[4] <- 4
tt[7] <- 3

And here is your new column:

> z$t * tt[z$x]
 [1] 21 44 23 96 25 26 81 28 29 30

> z$q <- z$t * tt[z$x]
> z
    x  y  t  q
1   1 11 21 21
2   2 12 22 44
3   3 13 23 23
4   4 14 24 96
5   5 15 25 25
6   6 16 26 26
7   7 17 27 81
8   8 18 28 28
9   9 19 29 29
10 10 20 30 30

This will not work if there are negative values in z$x.

Edited

Here is a generalization of the above, where a function is used to generate the multiplier vector. In fact, we create a function based on parameters.

We want to transform the following values:

2 -> 2
4 -> 4
7 -> 3

Otherwise a default of 1 is taken.

Here is a function which generates the desired function:

f <- function(default, x, y) {
  x.min <- min(x)
  x.max <- max(x)
  y.vals <- rep(default, x.max-x.min+1)
  y.vals[x-x.min+1] <- y

  function(z) {
    result <- rep(default, length(z))
    tmp <- z>=x.min & z<=x.max
    result[tmp] <- y.vals[z[tmp]-x.min+1]
    result
  }
}

Here is how we use it:

x <- c(2,4,7)
y <- c(2,4,3)

g <- f(1, x, y)

g is the function that we want. It should be clear that any mapping can be supplied via the x and y parameters to f.

g(z$x)
## [1] 1 2 1 4 1 1 3 1 1 1

g(z$x)*z$t
## [1] 21 44 23 96 25 26 81 28 29 30

It should be clear this only works for integer values.