What should I do if I want to devide data into 2 groups by certain percentile?

[ang]

I want to do binary logistic regression analysis, but the value that I wanna use as dependent variable is continuous form. So I guess I have to code this dependent variable data into 2 groups, 1 and 0.
What I want to set as criterion of division is 30%. Thus, I want to code 1 if the datum(row) belongs to upper 30% among the whole data while 0 if the datum belongs to under 30% among the whole data.
I've searched how to code this. There are lots of example that coding with certain constant for just by quntiles/decile, but few of certain exact ratio. What should I do?
I would be very appreciate if you tell me an example, supposing the name of the data is "glm_example", and the variable that I wanna devide is "exposure".

[fcas80]

Hi,

I want to code 1 if the datum(row) belongs to upper 30% among the whole data while 0 if the datum belongs to under 30% among the whole data.

I assume you mean 0 if the datum belongs to under 70% among the whole data.

glm_example <- data.frame(exposure=c(seq(1:10)))
q <- quantile(glm_example$exposure, .7)
glm_example$exposure_binary <- ifelse(glm_example$exposure <= q, 0, 1)
glm_example

exposure exposure_binary
1 1 0
2 2 0
3 3 0
4 4 0
5 5 0
6 6 0
7 7 0
8 8 1
9 9 1
10 10 1

[ang]

Thank youl. But it seems that you gave me an example under supposition there is a data composed of 1~10.
And I'm gonna analyze with my own data. In this situation I guess the first line wouldn't be needed, right?
Plus, isn't it right reversing the sequence of 0 and 1 on third line? Because if the logic is true, it returns 1, and if not it returns 0.

[fcas80]

Hi.

I don't have your data, so I composed an example with my data. So yes, you don't need my first line.

You said you want to return 1 if the row belongs to the upper 30%. My rows 8, 9, and 10 are greater than the 70% quantile, which is the same as being in the upper 30%, and so return 1.

If this is not exactly what you want, does this provide enough of an example so that you can change it to what you want?

[ang]

It was exactly helpful. I just wanted to confirm some details to apply to my code. Thank you so much