R help - Nov 2011 - Unexpected behavior when browsing list objects by name, when the object name is a substring (prefix) of an existing object that has a valid value

>
> Hi,
>
> The program I am writing requires me to append named objects to my
> existing list objects dynamically.
>
> So my list object is retval. retval always has a metadatatabletype object
>
> createMetadata=TRUE
> retval <-list()
> retval$metadatatype =c("normal")
> retval$metadata=NULL
>
> How, depending on certain logic, I create a metadata object
>
> if (createMetadata==TRUE) retval$metadata =rbind(retval$metadata,c(1,0) )
> The results are
> > retval$metadata
>      [,1]     [,2]
> [1,] "normal" "normal"
> [2,] "1"      "0"
>
>
> What I expected to see is
> > retval$metadata
>      [,1]     [,2]
> [1,] "1"      "0"
>
>
>
> I have been able to reproduce this problem only when the object
> retval$metadata is NULL and there is an existing object that has a valid
> value and the NULL object is a sub-string (prefix) of the existing object
> with a valid value.
>
> Also, retval$metadata takes on a value of "normal" even though it
has been
> explicity set as NULL
>
> Your assistance is appreciated.
>
> Thanks
> Vathaid
>
>
>
>
	[[alternative HTML version deleted]]

You've stumbled on one of the reasons use of the $ operator is
discouraged in formal programming: it uses partial matching when given
names.

E.g.,

a = list(boy = 1:5, cat = 1:10, dog = 1:3)

a$d #Exists

If you want to require exact matching (and it seems you do), use the
[[ operator.

a[["d"]] # Error
a[["dog"]] # Works
a[["alligator"]] <- 1:100  #Works

Michael

On Tue, Nov 8, 2011 at 12:29 AM, Val Athaide <vathaid at gmail.com>
wrote:
>>
>> Hi,
>>
>> The program I am writing requires me to append named objects to my
>> existing list objects dynamically.
>>
>> So my list object is retval. retval always has a metadatatabletype
object
>>
>> createMetadata=TRUE
>> retval <-list()
>> retval$metadatatype =c("normal")
>> retval$metadata=NULL
>>
>> How, depending on certain logic, I create a metadata object
>>
>> if (createMetadata==TRUE) retval$metadata =rbind(retval$metadata,c(1,0)
)
>> The results are
>> > retval$metadata
>> ? ? ?[,1] ? ? [,2]
>> [1,] "normal" "normal"
>> [2,] "1" ? ? ?"0"
>>
>>
>> What I expected to see is
>> > retval$metadata
>> ? ? ?[,1] ? ? [,2]
>> [1,] "1" ? ? ?"0"
>>
>>
>>
>> I have been able to reproduce this problem only when the object
>> retval$metadata is NULL and there is an existing object that has a
valid
>> value and the NULL object is a sub-string (prefix) of the existing
object
>> with a valid value.
>>
>> Also, retval$metadata takes on a value of "normal" even
though it has been
>> explicity set as NULL
>>
>> Your assistance is appreciated.
>>
>> Thanks
>> Vathaid
>>
>>
>>
>>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
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