Bound the values of a vector to a limit in R - r

Question

Suppose X is vector of length 100 with X position for 100 individuals. All agents start with position 0
X <- rep(0,100)
but they are embedded in a word with boundaries. I have a function that randomly changes the X position of all the agents at a given time.
Store <- X
X <- X + runif(100)
Eventually, one agent will reach the boundary and, at that point, it stay within the limits. The most simple way to do it using a looping through the vector and checking with if (in pseudo code):
for (i in 1:length(X)) {
if (between the boundaries) {keep the new X[i]} else {assign X[i] the value in Store[i]}
}
This is useful for 100 individual, but the for-loop adds too much computational time if the number of individual (and the length of the vector) increases, for example, to 1000000.
Is there a more straightforward way to do it? I was thinking that maybe I could skip specific re assignation of values that exceed the threshold during:
X <- X + runif(100)
EDIT: Also, imagine that X is not a vector but a matrix.

Answer 1

I realize this question is relatively old, but I just had the same question so I didn't want to leave it unanswered.
Limiting a vector or matrix to values within a certain range, can be done in a comprehensive way by combining an apply statement with min and max functions, as shown in the example below.
# Create sample vector
X <- c(1:100); print(X)
# Create sample matrix
M <- matrix(c(1:100),nrow=10); print(M)
# Set limits
minV <- 15; maxV <- 85;
# Limit vector
sapply(X, function(y) min(max(y,minV),maxV))
# Limit matrix
apply(M, c(1, 2), function(x) min(max(x,minV),maxV))
For further information on the apply functionality I would refer to the R documentation and this article on R-Bloggers:
https://www.r-bloggers.com/using-apply-sapply-lapply-in-r/
When I first came across apply statements I found it a difficult concept to wrap my head around, but would now consider it one of R's most powerful features.