I made a loop to generate a Markov Chain. If the proposal does not satisfy a condition, I want to restart the iteration with a new proposal? Is there a way to do this? My current code is shown below for reference. Currently, it sets the current chain's value to the previous one. But I don't want that. I want it to just restart the "i". So if i=2, and the condition in line 4 is not satisfied, I then want it to stay at i=2 until it is satisfied. Thanks in advance.
ABC_MCMC<-function(n){
for (i in 2:n){
prop<-rnorm(1,mean=chain[i-1],sd=1)
if (ABC(prop)==T & prop>=0){
h_ratio<-(dgamma(prop,shape=prior_alpha,rate=prior_beta)/dgamma(chain[i-1],shape=prior_alpha,rate=prior_beta))*
(dnorm(x=chain[i-1],mean=prop,sd=1)/dnorm(x=prop,mean=chain[i-1],sd=1))
u<-runif(1)
if (min(1,h_ratio)>u) {chain[i]=prop} else {chain[i]=chain[i-1]}
}
else{chain[i]=chain[i-1]}
}
return(chain<<-chain)
}
This is more of a comment than of an answer but to keep the code formatting I'm posting as an answer.
Replace the code inside the for loop for the code below.
while(TRUE) {
prop <- rnorm(1, mean = chain[i - 1L], sd = 1)
if (ABC(prop) && prop >= 0) {
h_ratio<-(dgamma(prop,shape=prior_alpha,rate=prior_beta)/dgamma(chain[i-1],shape=prior_alpha,rate=prior_beta))*
(dnorm(x=chain[i-1],mean=prop,sd=1)/dnorm(x=prop,mean=chain[i-1],sd=1))
u<-runif(1)
if (min(1,h_ratio)>u) {chain[i]=prop} else {chain[i]=chain[i-1]}
break
} else {chain[i] <- chain[i-1]}
}
Edit
The function below seems to be what is asked for.
ABC_MCMC <- function(n){
for (i in 2:n){
# loops until condition (ABC(prop) & prop >= 0) is met
while(TRUE) {
prop <- rnorm(1, mean = chain[i-1], sd = 1)
if (ABC(prop) & prop >= 0) {
h_ratio <- (dgamma(prop, shape = prior_alpha, rate = prior_beta)/dgamma(chain[i - 1L], shape = prior_alpha, rate = prior_beta)) *
(dnorm(chain[i - 1L], prop, 1)/dnorm(prop, chain[i - 1L], 1))
u <- runif(1)
if (min(1, h_ratio) > u) {
chain[i] <- prop
} else {
chain[i] <- chain[i - 1L]
}
break
}
}
}
# function return value
chain
}
Related
for (i in 2:100 )
{
count <- 0
for (j in i )
if( (i %% j ) == 0 )
count <- count + 1
if(count == 2 )
print(i)
}
I am trying to print print prime numbers in R. Could any one help me to resolve
Let us look at your code and show what went wrong. It's the inner loop that did not loop at all:
for (i in 2:100 )
{
count <- 0
for (j in 1:i ) # you forgot to provide a vector here
if( i %% j == 0 )
count <- count + 1
if(count == 2)
print(i)
}
The answer above tries to optimise the code some more and is a more efficient solution. For example does it only test odd numbers because even ones clearly aren't prime numbers.
The below code creates the function prime_numbers which returns prime numbers up to an inputted number.
prime_numbers <- function(n) {
if (n >= 2) {
x = seq(2, n)
prime_nums = c()
for (i in seq(2, n)) {
if (any(x == i)) {
prime_nums = c(prime_nums, i)
x = c(x[(x %% i) != 0], i)
}
}
return(prime_nums)
}
else {
stop("Input number should be at least 2.")
}
}
## return the answer to your question
prime_numbers(100)
If you wanted the range 3:100, after running the above code you could run something like this:
a<-prime_numbers(100)
a[a>3]
I hope this helps!
I am learning how to use while and for loops, and am having difficulty executing a for loop within a while loop. I am trying to recurse a simple procedure over a vector, and have the while loop set the conditionals for which parts of the vector are operated upon. This is really just meant as an exercise to understand how to use for and while loops in conjunction.
data <- c(1:200)
n=0
while(n < 100){
for(x in data){
n=x+1
if(x >= 10 & x < 100){
print("double digit")
} else {
print("single digit")
}}}
I want to stop the while loop when the procedure hits x=100 of the vector that runs from 1:200. But instead, the for loop runs through every element within the vector, from 1:200, failing to stop executing when n hits 100.
Would appreciate any advice to help out a new coder, thanks.
I have also tried
for(x in data){
n=x+1
while(n < 100){
if(x >= 10 & x < 100){
print("double digit")
} else {
print("single digit")
}}}
But the code does not stop executing.
First let's try a for loop. Each time through it n will be set to the loop counter plus 1. If this result is between 10 and 100, print a message, if not print something else. Note that no loop depends on n .
data <- c(1:200)
n = 0
for (x in data) {
n = x + 1
if (n < 100) {
if (x >= 10 && x < 100) {
print("double digit")
} else {
print("single digit")
}
}
}
x
#[1] 200
n
#[1] 201
Now for a while loop. I believe it is much simpler, it only envolves one variable, n.
n <- 0
while (n < 100) {
n = n + 1
if (n < 100) {
if (n >= 10) {
print("double digit")
} else {
print("single digit")
}
}
}
n
#[1] 100
I was asked to implement function that calculates n-dimensional matrix determinant using Laplace expansion. This involves recursion. I developed this:
minor<-function(A,i,j) {
return(A[c(1:(i-1),(i+1):dim(A)[1]),c(1:(j-1),(j+1):dim(A)[2])])
}
determinantRec<-function(X,k) {
if (dim(X)[1] == 1 && dim(X)[2] == 1) return(X[1][1])
else {
s = 0
for (i in 1:dim(X)[2]) {
s = s + X[k][i]*(-1)^(k+i)*determinantRec(minor(X,k,i),k)
}
return(s)
}
}
where k in determinantRec(X,k) function indicates which row I want to use Laplace expansion along of.
My problem is when I run determinantRec(matrix(c(1,2,3,4),nrow = 2,ncol = 2),1) this error appears:
C stack usage 7970628 is too close to the limit
What is wrong with my code?
#julia, there is one simple type in your code. Just remove the '*' at the end of the definition of 's'. And don't indent the recursion.
determinantRek<-function(X,k) {
if (dim(X)[1] == 1 && dim(X)[2] == 1)
return(X[1,1])
if (dim(X)[1] == 2 && dim(X)[2] == 2)
return(X[1,1]*X[2,2]-X[1,2]*X[2,1])
else
s = 0
for (i in 1:dim(X)[2]) {
s = s + X[k,i]*(-1)^(k+i)
determinantRek(X[-k,-i],k)
}
return(s)
}
I did this way and works just fine, although it is super slow, compared to the det function in base R
laplace_expansion <- function(mat){
det1 <- function(mat){
mat[1]*mat[4]-mat[2]*mat[3]
}
determinant <- 0
for(j in 1:ncol(mat)){
mat1 <- mat[-1,-j]
if(nrow(mat1) == 2){
determinant <- determinant+mat[1,j]*(-1)^(1+j)*det1(mat1)
}else{
val <- mat[1,j]*(-1)^(1+j)
if(val != 0){
determinant <- determinant+val*laplace_expansion(mat1)
}
}
}
return(determinant)
}
This is my approach, I think it's cleaner.
deter <- function(X) {
stopifnot(is.matrix(X))
stopifnot(identical(ncol(X), nrow(X)))
if (all(dim(X) == c(1, 1))) return(as.numeric(X))
i <- 1:nrow(X)
out <- purrr::map_dbl(i, function(i){
X[i, 1] * (-1)^(i + 1) * deter(X[-i, -1, drop = FALSE])
})
return(sum(out))
}
Thank you #ArtemSokolov and #MrFlick for pointing the problem cause, it was it. I also discovered that this code does not calculate properly the determinant of 2x2 matrix. After all it looks like that:
determinantRek<-function(X,k) {
if (dim(X)[1] == 1 && dim(X)[2] == 1)
return(X[1,1])
if (dim(X)[1] == 2 && dim(X)[2] == 2)
return(X[1,1]*X[2,2]-X[1,2]*X[2,1])
else
s = 0
for (i in 1:dim(X)[2]) {
s = s + X[k,i]*(-1)^(k+i)*
determinantRek(X[-k,-i],k)
}
return(s)
}
Debuging with browser() was also helpful :)
Following with this question R: from a vector, list all subsets of elements so their sum just passes a value
I´m trying to find a way to store the values given by the print command in a vector or matrix but I can´t find any way to do it.
The code is:
v<-c(1,2,3)
threshold <- 3 # My threshold value
recursive.subset <-function(x, index, current, threshold, result){
for (i in index:length(x)){
if (current + x[i] >= threshold){
print(sum(c(result,x[i])))
} else {
recursive.subset(x, i + 1, current+x[i], threshold, c(result,x[i]))
}
}
}
Many thanks in advance.
I tried this code but I just get the last sum
recursive.subset <-function(x, index, current, threshold, result){
for (i in index:length(x)){
if (current + x[i] >= threshold){
return(sum(c(result,x[i])))
} else {
m<-recursive.subset(x, i + 1, current+x[i], threshold, c(result,x[i]))
c(m,m)
}
}
}
thanks
Try this:
v<-c(1,2,3)
threshold <- 3 # My threshold value
recursive.subset <-function(x, index, current, threshold, result){
for (i in index:length(x)){
if (current + x[i] >= threshold){
store <<- append(store, sum(c(result,x[i])))
} else {
recursive.subset(x, i + 1, current+x[i], threshold, c(result,x[i]))
}
}
}
store <- list()
inivector <- vector(mode="numeric", length=0) #initializing empty vector
recursive.subset (v, 1, 0, threshold, inivector)
The problem in your solution is the position of "return" statement. The solution could be:
recursive.subset2 <-function(x, index, current, threshold, result){
m <- NULL
for (i in index:length(x)){
if (current + x[i] >= threshold){
m <- c(m, sum(c(result,x[i])))
} else {
m <- c(m, recursive.subset2(x, i + 1, current+x[i], threshold, c(result,x[i])))
}
}
return(m)
}
I have been trying to run this code (below here) and I have gotten that message "Error in if (temp[ii] == 0) { : missing value where TRUE/FALSE needed"...
temp = c(2.15, 3.5, 0, 0, 0, 1.24, 5.42, 6.87)
tm = length(temp)
for (i in 1:tm){
if (temp[i] == 0) {
counter3 = 1
last = temp[i - 1]
for (ii in i + 1:tm){
if (temp[ii] == 0) {
counter3 = counter3 + 1
}
if (temp[ii] != 0) {
nxt = temp[i + counter3]
}
}
}
}
Your problem is that temp[ii] is returning NA because ii goes out of bounds:
ii = i + 1:tm #Your declaration for ii
ii = 1:tm + 1:tm #Evaluates to
So ii will definitely be larger than tm (and therefore length(temp) at some point.
In order to better understand/debug for loops, consider printing just the indices:
for(i in 1:tm)
{
print(i)
for(ii in i + 1:tm)
print(ii)
}
At a guess I'm going to say that this is in R - if so I'm guessing that this line:
if (temp[i] == 0) (or temp[ii] == 0)
is resulting in an NA, and if conditions must have a TRUE or FALSE value.
Using a debugger if you can, I'd interrogate the value of temp[i] before the if block.
Difficult without knowing the language, but i think the issue is that the value in ii can be greater than the length of temp when i is at its upper bound. I'd have expected an index out of range or something similar but, without knowing the language, who knows! Hope you get your problem fixed.