Add an index (numeric ID) column to large data frame

You can add a sequence of numbers very easily with

data$ID <- seq.int(nrow(data))

If you are already using library(tidyverse), you can use

data <- tibble::rowid_to_column(data, "ID")

Using alternative dplyr package:

library("dplyr") # or library("tidyverse")

df <- df %>% mutate(id = row_number())

If your data.frame is a data.table, you can use special symbol .I:

data[, ID := .I]