# How to Add Points to an Existing Plot in R

You can use the points() function to add points to an existing plot in R.

This function uses the following basic syntax:

```points(df2\$x, df2\$y, col='red')
```

This particular syntax adds red points to an existing scatter plot in R using the variables called x and y from a data frame called df2.

The following example shows how to use this syntax in practice.

## Example: Add Points to an Existing Plot in R

Suppose we use the plot() function to create the following scatter plot in R:

```#create data frame
df1 <- data.frame(x=c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
y=c(4, 5, 5, 4, 6, 8, 12, 15, 19, 22))

#create scatterplot
plot(df1\$x, df1\$y, col='blue', pch=16)
``` Note: The col argument specifies the color of the points in the plot and the pch argument specifies the symbol to use. A value of 16 represents a filled-in circle.

Now suppose that we would like to add points from another data frame to the plot.

We can use the points() function to do so:

```#create second data frame
df2 <- data.frame(x=c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
y=c(14, 12, 9, 9, 8, 5, 4, 5, 3, 2))

#add points from df2 to the existing scatter plot
points(df2\$x, df2\$y, col='red', pch=16)
``` Notice that the points from the second data frame have been added to the existing plot and are represented by a red color.

If we’d like, we can also use the legend() function to add a legend to the plot so that we can distinguish which points came from which data frame:

```#add legend to plot
legend(x=1, y=22, legend=c('df1', 'df2'), fill=c('blue', 'red'))
``` Note: You can use the points() function as many times as you’d like to add points from as many data frames as you’d like to an existing plot.