How to get row index number in R

Question

Suppose I have a list or data frame in R  and I would like to get the row index  how do I do that  That is  I would like to know how many rows a certain matrix consists of

User · Answer

I m interpreting your question to be about getting row numbers     You can try as numeric rownames df   if you haven t set the rownames   Otherwise use a sequence of 1 nrow df     The which   function converts a TRUE FALSE row index into row numbers

User · Answer

See row in  base  row  This gives the row indices for any matrix-like object

User · Answer

rownames dataframe    This will give you the index of dataframe

User · Answer

If i understand your question  you just want to be able to access items in a data frame  or list  by row   x   matrix  ceiling 9 runif 20    nrow 5       colnames x    c  col1    col2    col3    col4   df   data frame x         create a small data frame  df 1                      get the first row df 3                      get the third row df nrow df                get the last row  lf   as list df           lf  1                     get first row lf  3                     get third row   etc

User · Answer

It not quite clear what exactly you are trying to do   To reference a row in a data frame use df row    To get the first position in a vector of something use match item vector   where the vector could be one of the columns of your data frame  eg df cname if the column name is cname   Edit   To combine these you would write   df match item df cname     Note that the match gives you the first item in the list  so if you are not looking for a unique reference number  you may want to consider something else

User · Answer

Perhaps this complementary example of  match  would be helpful   Having two datasets    first dataset  lt - data frame name   c  John    Luke    Simon    Gregory    Mary                                role   c  Audit    HR    Accountant    Mechanic    Engineer     second dataset  lt - data frame name   c  Mary    Gregory    Luke    Simon      If the name column contains only unique across collection values  across whole collection  then you can access row in other dataset by value of index returned by match  name mapping  lt - match second dataset name  first dataset name    match returns proper row indexes of names in first dataset from given names from second      5 4 2 1 example here - accesing roles from first dataset by row index  by given name value   for i in 1 length name mapping         role  lt - as character first dataset role name mapping i           second dataset role i    role          second dataset with new column       name       role 1    Mary   Engineer 2 Gregory   Mechanic 3    Luke Supervisor 4   Simon Accountant   r

[r] How to get row index number in R?

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