I have a data frame with a number of columns. I would like to create a new column called “id” that gives a unique id number to each group of identical values in the “sample” column.
Example data:
# dput(df)
df <- structure(list(index = 1:30, val = c(14L, 22L, 1L, 25L, 3L, 34L,
35L, 36L, 24L, 35L, 33L, 31L, 30L, 30L, 29L, 28L, 26L, 12L, 41L,
36L, 32L, 37L, 56L, 34L, 23L, 24L, 28L, 22L, 10L, 19L), sample = c(5L,
6L, 6L, 7L, 7L, 7L, 8L, 9L, 10L, 11L, 11L, 12L, 13L, 14L, 14L,
15L, 15L, 15L, 16L, 17L, 18L, 18L, 19L, 19L, 19L, 20L, 21L, 22L,
23L, 23L)), .Names = c("index", "val", "sample"), class = "data.frame",
row.names = c(NA, -30L))
head(df)
index val sample
1 1 14 5
2 2 22 6
3 3 1 6
4 4 25 7
5 5 3 7
6 6 34 7
What I would like to end up with:
index val sample id
1 1 14 5 1
2 2 22 6 2
3 3 1 6 2
4 4 25 7 3
5 5 3 7 3
6 6 34 7 3
How about
df2 <- transform(df,id=as.numeric(factor(sample)))
?
I think this (cribbed from Creating a unique ID) should be slightly more efficient, although perhaps a little harder to remember:
df3 <- transform(df, id=match(sample, unique(sample)))
all.equal(df2,df3) ## TRUE