R help - Nov 2021 - R lattice contourplot: select only specific values

I have a dataframe of three variables: x, y, z. The value of z are:
```
> unique(df$z)
[1] 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.6 3.0 2.4 2.8
```
I would like to plot the contour where the data get integer values
(1.0, 2.0, 3.0) but also highlight where the 1.8 and 2.8 values
occurred. Thus, I am plotting the data with lattice's contourplot with
a cut of 3,  and I would like to add a layer with the contours for the
2.8 values. A sort of mean and 95% CI margins around it.
I selected a subset of the original dataframe, but it does not plot anything.
```
library(lattice)
library(latticeExtra)
ds = subset(df, z == 1.8 | z == 2.8)
a = contourplot(z ~ y*x, data = df, cuts = 3, lwd = 3, labels=FALSE)
b = contourplot(Class ~ y*x, data = ds, lwd = 1, col="blue")
P = a + as.layer(b)
print(P)
```

Is there a way to select only a subset of the contours? If I increase
`cuts` I get more levels, I am only interested in certain values...
Thank you

Try using at=c(1.8, 2.8) to specify the contour levels you want (and omit
the cuts= argument).

-Bill

On Wed, Nov 17, 2021 at 5:41 AM Luigi Marongiu <marongiu.luigi at
gmail.com>
wrote:
> I have a dataframe of three variables: x, y, z. The value of z are:
> ```
> > unique(df$z)
> [1] 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.6 3.0 2.4 2.8
> ```
> I would like to plot the contour where the data get integer values
> (1.0, 2.0, 3.0) but also highlight where the 1.8 and 2.8 values
> occurred. Thus, I am plotting the data with lattice's contourplot with
> a cut of 3,  and I would like to add a layer with the contours for the
> 2.8 values. A sort of mean and 95% CI margins around it.
> I selected a subset of the original dataframe, but it does not plot
> anything.
> ```
> library(lattice)
> library(latticeExtra)
> ds = subset(df, z == 1.8 | z == 2.8)
> a = contourplot(z ~ y*x, data = df, cuts = 3, lwd = 3, labels=FALSE)
> b = contourplot(Class ~ y*x, data = ds, lwd = 1, col="blue")
> P = a + as.layer(b)
> print(P)
> ```
>
> Is there a way to select only a subset of the contours? If I increase
> `cuts` I get more levels, I am only interested in certain values...
> Thank you
>
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