Maximum values in plot

Question

[Grunir112]

I have a plot,where y-axis are obervations and x-axis is time. I have to find the maximun (x,y point) from the plot. I used max(), but I only figured out the obervation value but not the time point where this max obervation value is. Could someone help me please?

[WouterDeCoster]

And how is the data structured? You can probably find this easier in your original dataframe/matrix than in a plot.

[ddiez]

Take a look at ?which.max and maybe ?max.col functions in R.

Answer 1

[zx8754]

Try this example, using base plot:

# dummy data
df1 <- mtcars[1:10, 1:2]

# plot
plot(df1$mpg, df1$cyl)

# get the max on y, and matching x value
df1Max <- df1[ which(max(df1$cyl) == df1$cyl), ]

# mark the max point on the plot
points(df1Max$mpg, df1Max$cyl, col = "red", pch = 19)

# add vertical line
abline(v = df1Max$mpg, col = "blue", lty = "dashed")