[R] dplyr and function length()

[Karl Schilling]

Dear Jeff:

No, the effect I described has nothing to do wit USING dplyr. It occurs 
with any (preexisting) data.frame once dplyr is LOADED (require(dplyr). 
It is this silent, sort of "backward acting" effect that disturbs me.

Best,

Karl Schilling

On 04.08.2015 12:20, Jeff Newmiller wrote:
> I can confirm that the drop default is different, but keep in mind that it is only changed for a tbl_df so just convert back to data.frame at the end of your dplr operations to get back to your familiar data.frame behavior.
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> Sent from my phone. Please excuse my brevity.
>
> On August 4, 2015 5:06:44 AM EDT, peter dalgaard<pdalgd at gmail.com>  wrote:
>> >
>> >On 04 Aug 2015, at 10:50 , Karl Schilling<karl.schilling at uni-bonn.de>
>> >wrote:
>> >
>>> >>Dear All,
>>> >>
>>> >>I have an observation / question about how the function length()
>> >works once package dplyr is loaded.
>>> >>
>>> >>Say we have a data.frame  df with n rows and m columns. Then a way to
>> >get the number of rows is to use
>>> >>
>>> >>length(df$m1)  (m1 here stand is as the header of the first column)
>>> >>
>>> >>or, alternatively
>>> >>
>>> >>length(df[,1]).
>>> >>
>>> >>Both commands will return n.
>>> >>
>>> >>However, once dplyr is loaded,
>>> >>
>>> >>length(df[,1]) will return a value of 1.
>>> >>
>>> >>length(df$m1) and also length(df[[1]]) will correctly return n.
>>> >>
>>> >>I know that using length() may not be the most elegant or efficient
>> >way to get the value of n. However, what puzzles (and somewhat
>> >disturbs) me is that loading of dplyr affects how length() works,
>> >without there being a warning or masking message upon loading it.
>>> >>
>>> >>Any clarification or comment would be welcome.
>> >
>> >Presumably, dplyr changes how [.data.frame works (by altering the
>> >default for drop=, I expect) so that df[,1] is a data frame with 1
>> >variable and not a vector. And yes, that_is_  somewhat disturbing.
>> >
>> >-pd
>> >
>>> >>
>>> >>Thank you so much,
>>> >>
>>> >>Karl
>>> >>
>>> >>
>>> >>--
>>> >>Karl Schilling
>>> >>

-- 
Karl Schilling