Hello,

Say I have a matrix of size 100x2

X = ( (x_1, y_1),

(x_2, y_2),

...,

(x_100, y_100))

Each entry (x_i, y_i) is a point of the unit circle.

How can I get a 2D plot of this matrix?

Hello,

Say I have a matrix of size 100x2

X = ( (x_1, y_1),

(x_2, y_2),

...,

(x_100, y_100))

Each entry (x_i, y_i) is a point of the unit circle.

How can I get a 2D plot of this matrix?

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I'm not sure if I understand you correctly because you are not providing a **REPR**oducible **EX**ample (reprex). Is this what you are trying to do?

```
library(ggplot2)
# Made up X matrix
X <- matrix(1:100, nrow = 50, ncol = 2)
X <- as.data.frame(X)
names(X) <- c("x", "y")
head(X)
#> x y
#> 1 1 51
#> 2 2 52
#> 3 3 53
#> 4 4 54
#> 5 5 55
#> 6 6 56
# Plot
ggplot(X, aes(x = x, y = y)) +
geom_point()
```

^{Created on 2019-04-07 by the reprex package (v0.2.1.9000)}

1 Like

I have 100 couples (x_i, y_i) in a matrix such that x_i^2 + y_i^2 = 1 and I want to plot them.

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Well, my code above is plotting (x, y) points, you can modify the code to do the same with your own matrix, if you want more specific help, please provide a reproducible example.

If you've never heard of a reprex before, you might want to start by reading this FAQ:

1 Like

If you have the coordinates of the points you want to plot in two columns of a matrix, you can simply use the `plot`

function on that matrix. You don't need to use `ggplot`

here. But of course, you can use it.

See below:

```
r <- 1
theta <- seq(from = -pi,
to = pi,
length.out = 1e+3)
u <- (r * cos(x = theta))
v <- (r * sin(x = theta))
data_in_matrix <- cbind(u, v)
# base plot function
plot(data_in_matrix,
asp = 1)
# using ggplot2
library(ggplot2)
```

```
# quickplot
quickplot(x = u,
y = v,
data = as.data.frame(x = data_in_matrix))
```

```
# ggplot
ggplot(data = as.data.frame(x = data_in_matrix),
mapping = aes(x = u,
y = v)) +
geom_point()
```

^{Created on 2019-04-07 by the reprex package (v0.2.1)}

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Thanks a lot, that was I was looking for.

Does it still work in dimension 3 e.g. for X = ( (x_1, y_1, z_1),

(x_2, y_2, z_2),

...,

(x_100, y_100, z_100))?

0 Likes

`ggplot2`

doesn't support 3D plotting but there are other options for this, like `plotly`

for example.

```
library(plotly)
plot_ly(data = X, x = ~x, y = ~y, z = ~z, type = "scatter3d", mode = "markers")
```

0 Likes

Thanks.

How did you resize your plots?

I get an "ellipse":

instead of a circle because the width is 4 times the height.

0 Likes

I tried the code:

Y = simuSphere(3, 10000)

Y = as.data.frame(Y)

names(Y) <- c("x", "y", "z")

plot_ly(data = Y, x = x, y = y, z = z, type = "scatter3d", mode = "markers")

where simuSphere(3, 10000) gives me a matrix like

but I got a 2D figure:

Do you know why?

0 Likes

You are missing this symbol `~`

```
plot_ly(data = Y, x = ~x, y = ~y, z = ~z, type = "scatter3d", mode = "markers")
```

0 Likes

To use same scale in both axes, use `coord_fixed`

.

You may wish to take a look at this SO thread:

1 Like

It's hard to know why without having a reproducible example, could you make one? I don't have access to the `simuSphere()`

function, so I can't test your code.

0 Likes

Sure, here is the code:

```
norme2 = function(x){
return(sqrt(sum(x^2)))
}
simuNormale = function(n) {
u = runif(n)
v = runif(n)
x = sqrt(-2*log(u))*sin(2*pi*v)
return(x)
}
simuSphere = function(d, n){
X = matrix(nrow = n, ncol = d)
for(i in 1:n){
N = simuNormale(d)
X[i,] = N/norme2(N)
}
return(X)
}
```

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I can't reproduce your issue, I get a 3D plot

```
library(plotly)
norme2 = function(x){
return(sqrt(sum(x^2)))
}
simuNormale = function(n) {
u = runif(n)
v = runif(n)
x = sqrt(-2*log(u))*sin(2*pi*v)
return(x)
}
simuSphere = function(d, n){
X = matrix(nrow = n, ncol = d)
for(i in 1:n){
N = simuNormale(d)
X[i,] = N/norme2(N)
}
return(X)
}
Y = simuSphere(3, 10000)
Y = as.data.frame(Y)
names(Y) <- c("x", "y", "z")
plot_ly(data = Y, x = ~x, y = ~y, z = ~z, type = "scatter3d", mode = "markers")
```

0 Likes

Weird, could it be a RStudio issue?

I've noticed that I don't get the plot for my graphics, I have to get them from Plots > save as image

0 Likes

I don't think so, try to run the code again on a fresh R session, `Ctrl`+`Shift`+`F10`

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I did that and also tried updating the plot ly library and restarting my computer but it didn't change anything

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Well, this seems like a different issue, I think you should ask this in a new topic (under #rstudio-ide category) and include all the relevant information to reproduce your problem including your R, RStudio and OS versions.

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