Create an ID (row number) column
RDataframeR FaqR Problem Overview
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
R Solutions
Solution 1 - R
Two [tag: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.
And another base R alternative:
d$ID <- seq_along(d[,1])
Solution 2 - R
You could use cbind
:
d <- data.frame(V1=c(23, 45, 56), V2=c(45, 45, 67))
## enter id here, you could also use 1:nrow(d) instead of rownames
id <- rownames(d)
d <- cbind(id=id, d)
## set colnames to OP's wishes
colnames(d) <- paste0("V", 1:ncol(d))
EDIT: Here a comparison of @dacko suggestions. d$id <- seq_len(nrow(d)
is slightly faster, but the order of the columns is different (id
is the last column; reorder them seems to be slower than using cbind
):
library("microbenchmark")
set.seed(1)
d <- data.frame(V1=rnorm(1e6), V2=rnorm(1e6))
cbindSeqLen <- function(x) {
return(cbind(id=seq_len(nrow(x)), x))
}
dickoa <- function(x) {
x$id <- seq_len(nrow(x))
return(x)
}
dickoaReorder <- function(x) {
x$id <- seq_len(nrow(x))
nc <- ncol(x)
x <- x[, c(nc, 1:(nc-1))]
return(x)
}
microbenchmark(cbindSeqLen(d), dickoa(d), dickoaReorder(d), times=100)
# Unit: milliseconds
# expr min lq median uq max neval
# cbindSeqLen(d) 23.00683 38.54196 40.24093 42.60020 47.73816 100
# dickoa(d) 10.70718 36.12495 37.58526 40.22163 72.92796 100
# dickoaReorder(d) 19.25399 68.46162 72.45006 76.51468 88.99620 100
Solution 3 - R
You could also do this using dplyr
:
DF <- mutate(DF, id = rownames(DF))
Solution 4 - R
Many presented their ideas, but I think this is the sortest and simplest code for this task:
data$ID <- 1:nrow(data)
One line. The one and only.
Solution 5 - R
data.table solution
Easier syntax and much faster
library(data.table)
dt <- data.table(V1=c(23, 45, 56), V2=c(45, 45, 67))
setnames(dt, c("V2", "V3")) # changing column names
dt[, V1 := .I] # Adding ID column
Solution 6 - R
Hope this will help. Shortest and best way to create ID column is:
dataframe$ID <- seq.int(nrow(dataframe))
Solution 7 - R
Here is a solution that keeps the dplyr piping format and places id in the first column, which may be preferred.
d %>%
mutate(id = rownames(.)) %>%
select(id, everything())
Solution 8 - R
If you're starting without named rows in your df, the tidy way is:
df %>%
mutate(id = row_number()) %>%
select(id, everything())
Solution 9 - R
The function rownames_to_column()
moves rownames into a column; found in the tidyverse
package (docs).
rownames_to_column(DF, "my_column_name")
Use column_to_rownames()
for the reverse operation.
Solution 10 - R
If your database is not too large this will work
# Load sample data
Dt1 <- tibble(V1=c(23,45,56),V2=c(45,45,67))
# Create Separate Tibble with row numbers
Dt2 <- tibble(id=seq(1:nrow(Dt1)))
# Join together
Dt3 <- cbind(Dt2,Dt1)