Is there a way to access an index within a vector

Question

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\

Answer 1

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

Answer 2

> 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)?

Answer 3

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.