r - Create an ID (row number) column

Question

I need to create a column with unique ID, basically add the row number as an own column. My current data frame looks like this:

   V1  V2
1  23  45
2  45  45
3  56  67

How to make it look like this:

V1  V2  V3
1  23  45
2  45  45
3  56  67

?

Many thanks

Answer 1

Two tidyverse alternatives (using sgibb's example data):

tibble::rowid_to_column(d, "ID")

which gives:

  ID V1 V2
1  1 23 45
2  2 45 45
3  3 56 67

Or:

dplyr::mutate(d, ID = row_number())

which gives:

  V1 V2 ID
1 23 45  1
2 45 45  2
3 56 67  3

As you can see, the rowid_to_column-function adds the new column in front of the other ones while the mutate&row_number()-combo adds the new column after the others.

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And another base R alternative:

d$ID <- seq_along(d[,1])