Does dplyr::row_number() calculate row number for each obs? If so, how?












2















On the tidyverse website reference, I saw two usage mutate(mtcars, row_number() == 1L) and mtcars %>% filter(between(row_number(), 1, 10)). It would be straight forward to think that the row_number() function is return the row number for each observation in the dataframe.



However, it has been emphasized in the documentation that the function is a window function and is similar to sortperm in other languages. As in the example:



x <- c(5, 1, 3, 2, 2, NA)

row_number(x)

# [1]  5  1  4  2  3 NA


May I ask if this function is intended to report the row number for each observations? If it is, what is the logic flow behind the function call?



Thanks!






r dplyr row-number







share|improve this question





























    2















    On the tidyverse website reference, I saw two usage mutate(mtcars, row_number() == 1L) and mtcars %>% filter(between(row_number(), 1, 10)). It would be straight forward to think that the row_number() function is return the row number for each observation in the dataframe.



    However, it has been emphasized in the documentation that the function is a window function and is similar to sortperm in other languages. As in the example:



    x <- c(5, 1, 3, 2, 2, NA)
    
row_number(x)
    
# [1]  5  1  4  2  3 NA


    May I ask if this function is intended to report the row number for each observations? If it is, what is the logic flow behind the function call?



    Thanks!






    r dplyr row-number







    share|improve this question



























      2












      2








      2








      On the tidyverse website reference, I saw two usage mutate(mtcars, row_number() == 1L) and mtcars %>% filter(between(row_number(), 1, 10)). It would be straight forward to think that the row_number() function is return the row number for each observation in the dataframe.



      However, it has been emphasized in the documentation that the function is a window function and is similar to sortperm in other languages. As in the example:



      x <- c(5, 1, 3, 2, 2, NA)
      
row_number(x)
      
# [1]  5  1  4  2  3 NA


      May I ask if this function is intended to report the row number for each observations? If it is, what is the logic flow behind the function call?



      Thanks!






      r dplyr row-number







      share|improve this question
















      On the tidyverse website reference, I saw two usage mutate(mtcars, row_number() == 1L) and mtcars %>% filter(between(row_number(), 1, 10)). It would be straight forward to think that the row_number() function is return the row number for each observation in the dataframe.



      However, it has been emphasized in the documentation that the function is a window function and is similar to sortperm in other languages. As in the example:



      x <- c(5, 1, 3, 2, 2, NA)
      
row_number(x)
      
# [1]  5  1  4  2  3 NA


      May I ask if this function is intended to report the row number for each observations? If it is, what is the logic flow behind the function call?



      Thanks!






      r dplyr row-number




      r dplyr row-number






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Jan 3 at 0:44









      Julius Vainora

      38.2k76685




      38.2k76685










      asked Jan 3 at 0:05









      DanielDaniel

      304




      304
























          1 Answer
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          2














          As ?row_number says, row_number is equivalent to rank(ties.method = "first"), where rank (see ?rank) returns the sample ranks of the values in a vector and using "first" results in a permutation with increasing values at each index set of ties:



          row_number
          
# function (x) 
          
# rank(x, ties.method = "first", na.last = "keep")
          
# <bytecode: 0x108538478>
          
# <environment: namespace:dplyr>


          So,



          x <- c(5, 1, 3, 2, 2, NA)
          
row_number(x)
          
# [1]  5  1  4  2  3 NA
          
rank(x, ties = "first", na.last = "keep") # I added na.last = "keep" to fully replicate row_number
          
# [1]  5  1  4  2  3 NA


          since



          sort(x)
          
# [1] 1 2 2 3 5


          and we gave a lower rank to the first 2 due to ties = "first".



          Now when we use simply row_number() in filter, mutate calls, then indeed it seems to simply return a vector of row numbers, as can be found here.






          share|improve this answer

























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            active

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            2














            As ?row_number says, row_number is equivalent to rank(ties.method = "first"), where rank (see ?rank) returns the sample ranks of the values in a vector and using "first" results in a permutation with increasing values at each index set of ties:



            row_number
            
# function (x) 
            
# rank(x, ties.method = "first", na.last = "keep")
            
# <bytecode: 0x108538478>
            
# <environment: namespace:dplyr>


            So,



            x <- c(5, 1, 3, 2, 2, NA)
            
row_number(x)
            
# [1]  5  1  4  2  3 NA
            
rank(x, ties = "first", na.last = "keep") # I added na.last = "keep" to fully replicate row_number
            
# [1]  5  1  4  2  3 NA


            since



            sort(x)
            
# [1] 1 2 2 3 5


            and we gave a lower rank to the first 2 due to ties = "first".



            Now when we use simply row_number() in filter, mutate calls, then indeed it seems to simply return a vector of row numbers, as can be found here.






            share|improve this answer






























              2














              As ?row_number says, row_number is equivalent to rank(ties.method = "first"), where rank (see ?rank) returns the sample ranks of the values in a vector and using "first" results in a permutation with increasing values at each index set of ties:



              row_number
              
# function (x) 
              
# rank(x, ties.method = "first", na.last = "keep")
              
# <bytecode: 0x108538478>
              
# <environment: namespace:dplyr>


              So,



              x <- c(5, 1, 3, 2, 2, NA)
              
row_number(x)
              
# [1]  5  1  4  2  3 NA
              
rank(x, ties = "first", na.last = "keep") # I added na.last = "keep" to fully replicate row_number
              
# [1]  5  1  4  2  3 NA


              since



              sort(x)
              
# [1] 1 2 2 3 5


              and we gave a lower rank to the first 2 due to ties = "first".



              Now when we use simply row_number() in filter, mutate calls, then indeed it seems to simply return a vector of row numbers, as can be found here.






              share|improve this answer




























                2












                2








                2







                As ?row_number says, row_number is equivalent to rank(ties.method = "first"), where rank (see ?rank) returns the sample ranks of the values in a vector and using "first" results in a permutation with increasing values at each index set of ties:



                row_number
                
# function (x) 
                
# rank(x, ties.method = "first", na.last = "keep")
                
# <bytecode: 0x108538478>
                
# <environment: namespace:dplyr>


                So,



                x <- c(5, 1, 3, 2, 2, NA)
                
row_number(x)
                
# [1]  5  1  4  2  3 NA
                
rank(x, ties = "first", na.last = "keep") # I added na.last = "keep" to fully replicate row_number
                
# [1]  5  1  4  2  3 NA


                since



                sort(x)
                
# [1] 1 2 2 3 5


                and we gave a lower rank to the first 2 due to ties = "first".



                Now when we use simply row_number() in filter, mutate calls, then indeed it seems to simply return a vector of row numbers, as can be found here.






                share|improve this answer















                As ?row_number says, row_number is equivalent to rank(ties.method = "first"), where rank (see ?rank) returns the sample ranks of the values in a vector and using "first" results in a permutation with increasing values at each index set of ties:



                row_number
                
# function (x) 
                
# rank(x, ties.method = "first", na.last = "keep")
                
# <bytecode: 0x108538478>
                
# <environment: namespace:dplyr>


                So,



                x <- c(5, 1, 3, 2, 2, NA)
                
row_number(x)
                
# [1]  5  1  4  2  3 NA
                
rank(x, ties = "first", na.last = "keep") # I added na.last = "keep" to fully replicate row_number
                
# [1]  5  1  4  2  3 NA


                since



                sort(x)
                
# [1] 1 2 2 3 5


                and we gave a lower rank to the first 2 due to ties = "first".



                Now when we use simply row_number() in filter, mutate calls, then indeed it seems to simply return a vector of row numbers, as can be found here.







                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited Jan 3 at 0:43

























                answered Jan 3 at 0:25









                Julius VainoraJulius Vainora

                38.2k76685




                38.2k76685
































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