[R] add one variable to a data frame

Ding, Yuan Chun ycd|ng @end|ng |rom coh@org
Fri May 11 21:04:45 CEST 2018

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

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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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