[R] how to assign a value?

[Jinsong Zhao]

On 2011-12-12 10:58, David Winsemius wrote:
>
> On Dec 11, 2011, at 9:07 PM, Jinsong Zhao wrote:
>
>> On 2011-12-12 0:00, David Winsemius wrote:
>>>
>>> On Dec 11, 2011, at 10:27 AM, Jinsong Zhao wrote:
>>>
>>>> Hi there,
>>>>
>>>> I hope to modify values in a vector or matrix in the following code:
>>>>
>>>> for (i in 1:9) {
>>>> assign(paste("a.", i, sep = ""), 1:i)
>>>> get(paste("a.", i, sep = ""))[i] <- i+50
>>>> }
>>>
>>> Just one matrix? Then you seem to have inappropriately borrowed using
>>> "." as an indexing operation. In R that is just another character when
>>> used as an object name. "a.1" is notgoing to evaulate to a[1]. Look at
>>> what you would have had after
>>>
>>> > for (i in 1:9) {
>>> + assign(paste("a.", i, sep = ""), 1:i)
>>> + }
>>> > ls()
>>> [1] "a" "a.1" "a.2"
>>> [4] "a.3" "a.4" "a.5"
>>> [7] "a.6" "a.7" "a.8"
>>> [10] "a.9"
>>>
>>> > a.1
>>> [1] 1
>>> > a.2
>>> [1] 1 2
>>>
>>> Each of those assign() operations created a single vector of length i. I
>>> doubt that was what you intended,
>>
>> yes, it was what I intended.
>
> Then you are free to continue banging your head against a wall.
>
>>
>>>
>>> Better would be to describe your objects and your intentions, rather
>>> than expecting us to understand your goals by just looking at code that
>>> doesn't achieve thos goals. (There is no `get<-` function which was the
>>> source of the error.)
>>>
>>
>> The question is why
>>
>> get(paste("a.", i, sep = ""))[i] <- i+50
>>
>> give the following error message:
>
> What part of THERE IS NO "get<-" function (much less a `get[<-`
> function) don't you understand?

Sorry, I didn't understand it in the previous post. Now, it seems clear...

>
>>
>> Error in get(paste("a.", i, sep = ""))[i] <- i + 50 :
>> target of assignment expands to non-language object
>>
>> The a.1 to a.9 was created in the previous step.
>>
>> if only
>>
>> get(paste("a.", i, sep = ""))[i]
>>
>> can give correct output.
>
> Right. They are there and can even be indexed:
>
>  > get(paste("a", 9, sep="."))[9]
> [1] 9
>
> You could assign the value of get(paste("a", 9, sep=".")) to an
> intermediate object, which you could then reference using "[" and then
> use `assign` to push that object's value back to an object named "a.1",
> , "a.2", etc. Very clumsy and not an idiom that people want to promote.
>
>  > x <- get(paste("a", 9, sep="."))
>  > x[9] <- x[9]+50
>  > assign(paste("a", 9, sep="."), x)
>  > a.9
> [1] 1 2 3 4 5 6 7 8 59

Yes, the intermediate object could be used to archive my goal:

for (i in 1:9) {
    assign(paste("a", i, sep = "."), 1:i)
    x <- get(paste("a", i, sep = "."))
    x[[i]] <- x[[i]] + 50
    assign(paste("a", i, sep = "."), x)
}

>
>
>> Why I cannot assign values to it?
>
> Using get, you mean? Because that is not the way R is designed. get()
> returns a value. `assign` is used... wait for it ... assignment.
>
>  > get(paste("a", 1, sep="."))
> [1] 1
>
> Not a.1 but rather a.1's value. You cannot assign something else to the
> number 1. You are free to complain about the fact that R is is not
> languageX as much as you like, but it won't create new capabilities for
> functions. You've been given advice about how to get to the goal you
> desire by both Dunlap and Burns. The counter-question is why you have
> such trouble accepting advice.
>

I don't have trouble accepting advice. I am just curious about the 
error. Thank you very much for your patience.

>>
>> Regards,
>> Jinsong
>
> David Winsemius, MD
> West Hartford, CT
>
>

Regards,
Jinsong