Is there a way to access an index within a vector

i need to access an index (individual value) within a vector. I assumed it would be similar to:

v1 <- c(a,b,c,d,e)
v1[3] = h

But that doesn't seem to work at all, anyone else know how to do this?

[EDIT] Ok to answer some of your questions, here is the larger picture of what i am trying to achieve overall:

MyDataR1 <- scan("myd1.txt",what='character') 
MyDataR2 <- scan("myd2.txt",what='character') 
MyDataR3 <- scan("myd3.txt",what='character')
MyDataR4 <- scan("myd4.txt",what='character') 

AmpsR1 <- vector(mode='numeric',length=length(MyDataR1)-1)
AmpsR2 <- vector(mode='numeric',length=length(MyDataR2)-1)
AmpsR3 <- vector(mode='numeric',length=length(MyDataR3)-1)
AmpsR4 <- vector(mode='numeric',length=length(MyDataR4)-1)

AmpsR <- list(AmpsR1,AmpsR2,AmpsR3,AmpsR4)
DatesR <- list(DatesR1,DatesR2,DatesR3,DatesR4)
MyDataR <- list(MyDataR1,MyDataR2,MyDataR3,MyDataR4)

for (m in 1:length(MyDataR)){
mode(MyDataR[m])
length(MyDataR[m])
for (i in 2:length(MyDataR[m])){ 
temp <- unlist(strsplit(MyDataR[[m]][i],',')) 
DatesR[[m]][i-1] <- temp[2] 
if (length(temp) == 7) 
AmpsR[[m]][i-1] <- as.numeric(temp[6]) 
else 
AmpsR[[m]][i-1] <- NA 

end 

(I changed my tactic at one point to use the "c()" function instead of creating lists, however that didn't work either). So i'm trying to iterate between each value of each vector in the list and set it's value, however when i print "AmpsR" after the for loo开发者_StackOverflow社区p section, all the values are "0.000". I know the data it is reading is valid as when i print "MyDataR1" it is filled with all the relevant values.

Any ideas or suggestions of a better way for doing this?? Thanks for your input everyone.

[EDIT] Apologies for the similar post I added when asking another question, it was just that this question didn't directly address the issue I was having. Regardless looking at the answers from both of them I've now gained a better understanding of how lists and vectors work and I managed to solve my issue (solution very similar to what Andrie answered with).

Thanks for your help everyone.

It's not obvious from your question exactly what your problem is, but I'll guess it's one of the following:

1. You are not quoting your strings properly.
2. You are using variables that don't exist.
3. You actually meant to create a list, not a concatenated vector

Option 1: Use quote marks to indicate character vectors (strings)

v1 <- c("a", "b", "c", "d", "e")
v1[3] <- "h"
v1
[1] "a" "b" "h" "d" "e"

Option 2: You haven't defined your variables a-e and h

> a <- 1
> b <- 2
> c <- 3
> d <- 4
> e <- 5
> h <- 8
> v1 <- c(a,b,c,d,e)
> v1[3] = h
> v1
[1] 1 2 8 4 5

Option 3: You meant to create and subset a list

In this case you should use list instead of c. And remember that you index a list using double square brackets.

a <- 1:5
b <- 6:10
c <- 11:15
d <- 16:20
e <- 21:25
h <- 26:30
v1 <- list(a,b,c,d,e)
v1[[3]] <- h

The list:

v1
[[1]]
[1] 1 2 3 4 5

[[2]]
[1]  6  7  8  9 10

[[3]]
[1] 26 27 28 29 30

[[4]]
[1] 16 17 18 19 20

[[5]]
[1] 21 22 23 24 25

Element 3 of the list:

v1[[3]]
[1] 26 27 28 29 30

> v1 <- c(1,2,3)
> v1[1] <- 5
> v1
[1] 5 2 3

Um, that should work. I'm not sure that it's clear what your problem is. In your example, are a,b,c,d,e and h all defined? Or should you be using them as strings (ie "a", "b", etc)?

If you have four vectors: v1, v2, v3, v4. then there are (at least) two ways to sequentially access them:

The hard way (IMO):

for ( i in 1:4 ) {print( get(paste("v", i, sep="") ) ) }

The right way (also IMO):

vlist <- list(v1, v2, v3, v4)
for (v in vlist) print(v)

In your revision it appears you constructed a third way:

vlist <- list(v1, v2, v3, v4)
for (v in 1:length(v) ) print( vlist[v] )

... which I would say was intermediate in right-ness between the first two constructions. The other thing you need to learn is that within a loop you need to DO SOMETHING to the values. Just putting mode(item) in the middle of the loop body will not produce any results. You need to assign it to a name or print it or ... something. Some of the commands you made are "doing something", but in the absence of a description of how they are failing to deliver what you expect and without the data, there not much that anyone can do to help further.