Hello, here's a more reproducible example.
I have an R script that borrows heavily from this blogpost and I'm trying to make some modifications to how the matrix of each simulation is constructed.
I'm really bad with for-loops in R, so I need a little help figuring it out.
What I'm hoping to do is find a way to inject a value to (re-baseline) for a certain row (or rows) ... maybe I'm over thinking this and missing something obvious?
# starting cash for each "simulation"
principle = 100
#starting inflation assumption
inflation = .05
#starting returns
returns = .02
# number of time units (lets say months)
n.obs = 5
# number of simulations (columns)
n.sim = 5
# time I retire and get access to 401k
t_retire = 4
# amount of money available to be added to my principal at t==t_retire
retire = 100
# simulate cases - they're all the same in this example
nav = matrix(start.capital, n.obs + 1, n.sim)
for (j in 1:n.obs) {
nav[j + 1, ] = (nav[j, ] * (1 + returns - inflation))
}
I want to edit this for-loop to add the "retire" value to my existing "principle" at row (t_retire) = 4.
With the minimal example I think this might be what is desired:
nav = matrix(start.capital, n.obs + 1, n.sim)
for (j in 1:n.obs) { if(j==t_retire){nav[j, ] <- nav[j-1, ] + retire}
nav[j + 1, ] = (nav[j, ] * (1 + returns - inflation))
}
nav
#----------------------
[,1] [,2] [,3] [,4] [,5]
[1,] 100000.00 100000.00 100000.00 100000.00 100000.00
[2,] 97000.00 97000.00 97000.00 97000.00 97000.00
[3,] 94090.00 94090.00 94090.00 94090.00 94090.00
[4,] 94190.00 94190.00 94190.00 94190.00 94190.00
[5,] 91364.30 91364.30 91364.30 91364.30 91364.30
[6,] 88623.37 88623.37 88623.37 88623.37 88623.37
If it's not the desired modification then at least it may form the basis for clarification. Not that the R habit of filling rows with copies of single values is at work here.