[R] dplyr and function length()

[Jeff Newmiller]

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
>> 
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