[R] hash table access, vector access &c

[David Winsemius]

On Jul 5, 2011, at 2:10 PM, Sam Steingold wrote:

>> * David Winsemius <qjvafrzvhf at pbzpnfg.arg> [2011-07-05 13:21:57  
>> -0400]:
>> On Jul 5, 2011, at 12:53 PM, Sam Steingold wrote:
>>> I am confused by the way the indexing works.
>> Actually I suspect you may be confused by how factors work. See  
>> below.
>
> probably both :-(
>
> being a lisper, I thought about factors as lisp symbols (and thus
> thought that they would be accepted everywhere strings are).
>
>> Have you considered:
>>
>> ysmd.table[ as.character( ysmd$X.stock[[100]])  ]
>>
>> It appears that ysmd$X.stock[[100]] is a factor, and if so, you  
>> probably
>> want the character value that its numeric representation points to.
>
> indeed:
>
>> as.character(ysmd$X.stock[[100]])
> [1] "FLO"
>
> however,
>
>> ysmd.table[as.character(ysmd$X.stock[[100]])]
> <hash> containing 0 key-value pair(s).
>  NA : NULL
>
> so, as.character is not the answer.

My error. Note the difference in indexing functions. "[" is not "[["

>
>> ysmd.table[["FLO"]]
>    X.stock market.cap X52.week.low X52.week.high  
> X3.month.average.daily.volume
> 100     FLO  2.984e+09      15.3133          
> 22.37                       1021580
>    X50.day.moving.average.price
> 100                      21.3769

So you are here demonstrating that you should be using "[["

>
>> This is, of course, guesswork because you have not disclosed what
>> package hash` comes from, so I do not have the benefit of looking at
>> its help page.
>
> I just did this:
>
> library(hash);
> hash-2.0.1 provided by Open Data.


-- 

David Winsemius, MD
West Hartford, CT