R help - Jun 2025 - How to stratify data with multiple group simultaneously with R ggplot2?

I would like to plot multivariate data with ggplot2. I have multiple
groups that I need to account for: I have the `x` and `y` values, but
the data must be stratified also by `w` and `z`. I can group by either
`w` or `z`, but how can I group for both simultaneously?
In essence, in the example below, the legend should have two columns
(A and B) and five rows (which are already there since the data is
stratified by w). There should be 10 colors.
How can I do that?
Thank you
>>>>>>
```
df = data.frame(x = c(rep(1,5), rep(2,5), rep(3,5), rep(4,5)),
                                w = rep(letters[1:5],4),
                                z = c(rep(LETTERS[1],10), rep(LETTERS[2],10)),
                                y = rnorm(20),
                                stringsAsFactors = FALSE)
library(ggplot2)
ggplot(df, aes(x=x, y=y, colour=w, group=w)) +
  geom_line(linewidth=2) +
  ggtitle("A+B")
ggplot(df[df$z=="A",], aes(x=x, y=y, colour=w, group=w)) +
  geom_line(linewidth=2) +
  ggtitle("A")
ggplot(df[df$z=="B",], aes(x=x, y=y, colour=w, group=w)) +
  geom_line(linewidth=2) +
  ggtitle("B")
```

You can use group=interaction(w,z)... but in my experience that gets confusing
for the poor person trying to make sense of the plot. It is better to use
color=w, linetype=z or use facets for one of the grouping variables.

On June 7, 2025 11:21:32 PM PDT, Luigi Marongiu <marongiu.luigi at
gmail.com> wrote:
>I would like to plot multivariate data with ggplot2. I have multiple
>groups that I need to account for: I have the `x` and `y` values, but
>the data must be stratified also by `w` and `z`. I can group by either
>`w` or `z`, but how can I group for both simultaneously?
>In essence, in the example below, the legend should have two columns
>(A and B) and five rows (which are already there since the data is
>stratified by w). There should be 10 colors.
>How can I do that?
>Thank you
>
>>>>>>>
>```
>df = data.frame(x = c(rep(1,5), rep(2,5), rep(3,5), rep(4,5)),
>                                w = rep(letters[1:5],4),
>                                z = c(rep(LETTERS[1],10),
rep(LETTERS[2],10)),
>                                y = rnorm(20),
>                                stringsAsFactors = FALSE)
>library(ggplot2)
>ggplot(df, aes(x=x, y=y, colour=w, group=w)) +
>  geom_line(linewidth=2) +
>  ggtitle("A+B")
>ggplot(df[df$z=="A",], aes(x=x, y=y, colour=w, group=w)) +
>  geom_line(linewidth=2) +
>  ggtitle("A")
>ggplot(df[df$z=="B",], aes(x=x, y=y, colour=w, group=w)) +
>  geom_line(linewidth=2) +
>  ggtitle("B")
>```
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
https://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
-- 
Sent from my phone. Please excuse my brevity.

?s 07:21 de 08/06/2025, Luigi Marongiu escreveu:
> I would like to plot multivariate data with ggplot2. I have multiple
> groups that I need to account for: I have the `x` and `y` values, but
> the data must be stratified also by `w` and `z`. I can group by either
> `w` or `z`, but how can I group for both simultaneously?
> In essence, in the example below, the legend should have two columns
> (A and B) and five rows (which are already there since the data is
> stratified by w). There should be 10 colors.
> How can I do that?
> Thank you
> 
>>>>>>>
> ```
> df = data.frame(x = c(rep(1,5), rep(2,5), rep(3,5), rep(4,5)),
>                                  w = rep(letters[1:5],4),
>                                  z = c(rep(LETTERS[1],10),
rep(LETTERS[2],10)),
>                                  y = rnorm(20),
>                                  stringsAsFactors = FALSE)
> library(ggplot2)
> ggplot(df, aes(x=x, y=y, colour=w, group=w)) +
>    geom_line(linewidth=2) +
>    ggtitle("A+B")
> ggplot(df[df$z=="A",], aes(x=x, y=y, colour=w, group=w)) +
>    geom_line(linewidth=2) +
>    ggtitle("A")
> ggplot(df[df$z=="B",], aes(x=x, y=y, colour=w, group=w)) +
>    geom_line(linewidth=2) +
>    ggtitle("B")
> ```
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
https://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
Hello,

You can use the 4th variable to define facets. Like this?


ggplot(df, aes(x=x, y=y, colour=w)) +
   geom_line(linewidth=2) +
   facet_wrap(~ z, scales = "free_x") +
   ggtitle("A+B")


Hope this helps,

Rui Barradas



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