Divide a vector by different values based on the result of the division - r

Question

I have a Df like this:
x y z
<dbl> <dbl> <dbl>
1 408001.9 343 0
2 407919.2 343 0
3 407839.6 343 0
4 407761.2 343 0
5 407681.7 343 0
6 407599.0 343 0
7 407511.0 343 0
8 407420.5 343 0
9 407331.0 343 0
10 407242.0 343 0
11 407152.7 343 0
12 407062.5 343 0
13 406970.7 343 0
14 406876.6 342 0
15 406777.1 342 0
16 406671.0 342 0
17 406560.9 342 0
18 406449.4 342 0
19 406339.0 342 0
20 406232.5 342 0
... ... ... ...
with x decreasing.
And a vector like
vec=(a1, a2, a3, a4, a5, a6, ...)
with a1< a2< a3< a4...
Now I want to divide df$x by vec[1], what will give the same result (rounded) as for df$y.
But now, when the value in df$z drops by one to 342, I want to divide the value in df$x by vec[2] from then on, to get the new df$z values.
From here the result will be different from df$y, as for df$y the number to divide with is allways vec[1]and will not change
Every time the value I get for df$z drops by one, the next values for df$z shal be calculated with the corresponding vec[i] where i is the number of drops+1 so far
In the end I want a vector df$z, where the values are df$x / vec[i], where vec [i] depends on, what the last number of df$z is.
reproducible example:
test <- data.frame(x = sort((seq(500, 600, 2)), decreasing = T)
)
vec <- seq(10, 10.9, 0.03)
for(i in 1:31){
test[i+1] <- round(test$x/vec[i])
}
This will give you a df with one col for every value of vec, that test$x got divided by.
Now, in the end, my vector shall contain the values of col2 until the value in col2 drops from 60 to 59. Afterwards I want the values from col3 until the value in col3 drops below 59 to 58. Then I want the values from col4 and so on.
How can I achive this with any data(like mine above, which is not linear ditributed as this example.)
I tried some for and while loops, but none worked. I didn't even get close to what I want.
I think my problem is that I dont know how to make the condition depenent on a value(the value of df$z at point i), that I want to calculate in the same operation. I want to calculate the value of df$z[i] with the value of vec[t], that has been used so far. But if the value of df$z drops by one at a certain observation[i], the value of vec[t+1] shall be used for the division from then on.
Thanks for your help.

Answer 1

I hope I've understood what you are asking. This might be it...
test <- data.frame(x = sort((seq(500, 600, 2)), decreasing = T)
vec <- seq(10, 10.9, 0.03)
#this function determines the index of `vec` to use
xcol<-function(v){
x<-rep(NA,length(v))
x[1] <- 1
for(i in 2:length(v)){
x[i] <- x[i-1]
if(round(v[i]/vec[x[i]])<round(v[i-1]/vec[x[i]])){
x[i] <- x[i]+1
}
}
return(x)
}
test$xcol <- xcol(test$x)
test$z <- round(test$x/vec[test$xcol])
test
x xcol z
1 600 1 60
2 598 1 60
3 596 1 60
4 594 2 59
5 592 2 59
6 590 2 59
7 588 2 59
8 586 3 58
9 584 3 58
10 582 3 58
11 580 3 58
12 578 4 57
...