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:avigr...@verizon.net] Sent: Friday, July 2, 2021 5:14 PM To: Yuan Chun Ding <ycd...@coh.org>; r-help@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-boun...@r-project.org> On Behalf Of Yuan Chun Ding Sent: Friday, July 2, 2021 6:27 PM To: r-help@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 ---------------------------------------------------------------------- ------------------------------------------------------------ -SECURITY/CONFIDENTIALITY WARNING- This message and any attachments are intended solely for the individual or entity to which they are addressed. This communication may contain information that is privileged, confidential, or exempt from disclosure under applicable law (e.g., personal health information, research data, financial information). 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