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

[Yuan Chun Ding]

Hi Avi,

Thank you for your patient with me!!  

Your code below generated what I want.  
test %>%
  group_by(group1,group2) %>%
  mutate(count2 = ifelse(row_number()==1, TRUE, FALSE)) %>%
  ungroup()

your code reminded me of the SAS first. And last. Function.  I gave up SAS several years ago.

Ding
-----Original Message-----
From: Avi Gross [mailto:avigross using verizon.net] 
Sent: Friday, July 2, 2021 5:14 PM
To: 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

Ding,

Just to get you to stop asking, here is a solution I hope works.

In English, if you are asking that ONE instance of a duplicate be marked in a new column with TRUE or 1 while all remaining ones are marked as FALSE or
2 or whatever, that is easy enough. The method is to use the assistive function row_number() inside a grouped mutate() and only one item has a row number of 1 and all others higher.

If I load your test variable (see below) I can add another column I called
count2 fairly easily with this:

test %>%
  group_by(group1,group2) %>%
  mutate(count2 = ifelse(row_number()==1, TRUE, FALSE)) %>%
  ungroup()

The output matches your first count variable made by hand:

> test %>%
  +   group_by(group1,group2) %>% 
  +   mutate(count2 = ifelse(row_number()==1, TRUE, FALSE)) %>%
  +   ungroup()
# A tibble: 9 x 4
group1 group2 count count2
<chr>  <chr>  <dbl> <lgl> 
  1 g1     k1         1 TRUE  
2 g1     a2         1 TRUE  
3 g1     a2         2 FALSE 
4 g2     c5         1 TRUE  
5 g2     n6         2 TRUE  
6 g2     n6         2 FALSE 
7 g2     n6         2 FALSE 
8 g2     m10        3 TRUE  
9 g2     m10        3 FALSE

Now if you actually want to have a count of first and 2nd and third, it is even easier:

test %>%
  group_by(group1,group2) %>%
  mutate(counter = row_number()) %>%
  ungroup()

Unfortunately for you, my version of output suggest you made a mistake on the last row with g2/n6:

> test %>%
  +   group_by(group1,group2) %>% 
  +   mutate(counter = row_number()) %>%
  +   ungroup()
# A tibble: 9 x 4
group1 group2 count counter
<chr>  <chr>  <dbl>   <int>
  1 g1     k1         1       1
2 g1     a2         1       1
3 g1     a2         2       2
4 g2     c5         1       1
5 g2     n6         2       1
6 g2     n6         2       2
7 g2     n6         2       3
8 g2     m10        3       1
9 g2     m10        3       2

There are of course other ways to do such things but the above seems simple enough.

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Yuan Chun Ding
Sent: Friday, July 2, 2021 6:27 PM
To: r-help using r-project.org
Subject: [R] add a variable a data frame to sequentially count unique rows

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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