[R] add one variable to a data frame

MacQueen, Don m@cqueen1 @end|ng |rom ||n|@gov
Fri May 11 21:30:19 CEST 2018

Sarah's solutions are good, and here's another, even more basic:

tmp1 <- unique(dat1$B)
tmp2 <- seq_along(tmp1)
dat1$C <- tmp2[ match( dat1$B, tmp1) ]

> dat1
    N      B C
1   1 29_log 1
2   2 29_log 1
3   3 29_log 1
4   4 27_cat 2
5   5 27_cat 2
6   6  1_log 3
7   7  1_log 3
8   8  1_log 3
9   9  1_log 3
10 10  1_log 3
11 11  3_cat 4
12 12  3_cat 4

As a single line command:

dat1$C <- seq(length(unique(dat1$B)))[ match( dat1$B, unique(dat1$B) )]

Don MacQueen
Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
Lab cell 925-724-7509
On 5/11/18, 12:04 PM, "R-help on behalf of Ding, Yuan Chun" <r-help-bounces using r-project.org on behalf of ycding using coh.org> wrote:

    Hi Sarah,
    Thank you so much!! I got your good ideas.
    -----Original Message-----
    From: Sarah Goslee [mailto:sarah.goslee using gmail.com] 
    Sent: Friday, May 11, 2018 11:40 AM
    To: Ding, Yuan Chun
    Cc: r-help mailing list
    Subject: Re: [R] add one variable to a data frame
    [Attention: This email came from an external source. Do not open attachments or click on links from unknown senders or unexpected emails.]
    Here's one way to approach it, using the coercion of factor to numeric.
    Note that I changed your data.frame() statement to avoid coercing strings to factors, just to make it simpler to set the levels.
    dat1 <-data.frame(N=seq(1, 12,1), B=c("29_log","29_log", "29_log", "27_cat", "27_cat", "1_log", "1_log", "1_log", "1_log", "1_log", "3_cat", "3_cat"), stringsAsFactors=FALSE)
    dat1$C1 <- as.numeric(factor(dat1$B, levels=unique(dat1$B)))
    And here's a way using rle()
    dat1$C2 <- rep(seq_len(length(unique(dat1$B))),
    (That second will work even if B is a factor.)
    > dat1
        N      B C1 C2
    1   1 29_log  1  1
    2   2 29_log  1  1
    3   3 29_log  1  1
    4   4 27_cat  2  2
    5   5 27_cat  2  2
    6   6  1_log  3  3
    7   7  1_log  3  3
    8   8  1_log  3  3
    9   9  1_log  3  3
    10 10  1_log  3  3
    11 11  3_cat  4  4
    12 12  3_cat  4  4
    On Fri, May 11, 2018 at 1:52 PM, Ding, Yuan Chun <ycding using coh.org> wrote:
    > Hi All,
    > I have a data frame dat1:
    > dat1 <-data.frame(N=seq(1, 12,1), B=c("29_log","29_log", "29_log", "27_cat", "27_cat",
    >                                                                        "1_log", "1_log", "1_log", "1_log", "1_log",
    > "3_cat", "3_cat"))
    > Then I need to add one column or variable to reflect uniqueness of B variable in sequential order as below.
    > dat1$C <-c(1,1,1,2,2,3,3,3,3,3,4,4)
    > I only show 12 rows, my real data frame has over 1000 rows, I can not manually to add column C.
    > It should be easy, but I can not figure out. Can you help me?
    > Thanks,
    > Ding
    Sarah Goslee
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