[R] add a variable a data frame to sequentially count unique rows

[Jeff Newmiller]

I am not sure I understand... you are referring to files but we are not 
discussing files here. There are "input" and "output" phases yet to be 
dealt with that separate the analysis you do in R from the files 
themselves. We are discussing data frames here.

Regardless, you either have duplicates in your input (faulty data) or you 
do not have duplicates because there are additional distinguishing columns 
that you have not identified. (https://en.wikipedia.org/wiki/Primary_key)

The solution to the problem that you should not have involves making a 
sensible (not faulty) copy of your data, setting up the count column, and 
then joining the faulty data with the sensible data.

Note that the ordering of the result happens to be retained when using 
dplyr::left_join, but is not retained using most other join 
implementations (such as base::merge). There can be significant 
performance gains to be had by giving up on record ordering, which is one 
of the reasons why having a valid primary key can be so important.

library(dplyr)
lookup_df <- (   test
              %>% select( group1, group2 )
              %>% filter( !duplicated( . ) )
              %>% group_by( group1 )
              %>% mutate( count1 = seq.int( n() ) )
              %>% ungroup()
              )
ans <- left_join( test, lookup_df, by = c( "group1", "group2" ) )

  On Fri, 2 Jul 2021, Yuan Chun Ding wrote:

> Hi Jeff,
>
> Thank you for your quick response!!
> I made this following summary file, however, I want to add the count number sequentially into the original file, because I have several more columns to explain or annotate the first two columns.
>
> count_test <- test %>% group_by(group1 ) %>%summarise(Number_of_region = n_distinct(group2))
>
>
> Ding
> -----Original Message-----
> From: Jeff Newmiller [mailto:jdnewmil using dcn.davis.ca.us]
> Sent: Friday, July 2, 2021 3:36 PM
> To: r-help using r-project.org; Yuan Chun Ding <ycding using coh.org>; r-help using r-project.org
> Subject: Re: [R] add a variable a data frame to sequentially count unique rows
>
> It is poor analytical design to keep duplicates. If they are not duplicates then there should be a distinguishing additional column. IMO you should re-think your analysis rather than accomplish this short-term goal only to find down the road that this duplication causes future problems.
>
> On July 2, 2021 3:27:21 PM PDT, Yuan Chun Ding <ycding using coh.org> wrote:
>> Hi R users,
>>
>> In this test file,
>> test  <- data.frame(group1=c("g1", "g1", "g1", "g2", "g2", "g2", "g2",
>> "g2", "g2"),
>>       group2=c("k1", "a2", "a2", "c5", "n6", "n6", "n6", "m10","m10"),
>>       count= c( 1,     1,    2,   1,     2,   2,     2,    3,    3 ));
>>
>> I have group 1 and group2 variable and want to add the count variable
>> to sequentially count unique rows defined by group1 and group2.
>>
>> I hope to use the following functions in library (tidyverse),  No one
>> worked well.
>> test %>% group_by(group1, group2) %>% mutate(count = row_number()) test
>> %>% group_by(group1, group2) %>% mutate(count = 1:n()) test %>%
>> group_by(group1, group2) %>% mutate(count = seq_len(n())) test %>%
>> group_by(group1, group2) %>% mutate(count = seq_along(group1,
>> group2))
>>
>> Can you help me to make the third column in the test data frame?
>>
>> Thank you,
>>
>> Ding
>>
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>
> --
> Sent from my phone. Please excuse my brevity.
>

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