如何在数据帧 r 中查找特定行的索引

Question

I have a dataframe, A, which looks like this:

col 1   col2   col3
 NL      6       9
 UK      5       5
 US      9       7

and I have a dataframe, B, consisting of a subset of the rows of the large dataframe looking like this:

 col 1   col2   col3
 NL      6       9
 UK      5       5

Now, I want to find the indices of the rows from B in A, so it should return 1 and 2 . Does someone know how to do this?

EDIT Next, I also want to find the indices of the rows in A, when I have only the first two columns in B. So, in that case it should also return 1 and 2 . Anyone an idea how to do this?

Answer 1

Generally, match gets the index. In our case, an approach is to paste the rows together and get the index with match

match(do.call(paste, df2), do.call(paste, df1)

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If there are only subset of columns that are having the same column names, get the vector of column names with intersect , subset the datasets, do the paste and get the index with match

nm1 <- intersect(names(df1), names(df2))
match(do.call(paste, df2[nm1]), do.call(paste, df1[nm1]))

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Another option is join where we create a row index in both datasets, do a join and extract the row index

 library(dplyr)
 df2 %>%
    mutate(rn = row_number()) %>% 
   left_join(df2 %>% 
          mutate(rn = row_number()), by = c('col1', 'col2', 'col3')) %>% 
   pull(rn.y)