CODEWITHSUNDEEP
rggplot2curve-fittingsplinebest-fit-curve
eFF
eFF

Reputation: 277

Calculate y-value of curve maximum of a smooth line in R and ggplot2

I'm following up an old question addressed here:

calculate x-value of curve maximum of a smooth line in R and ggplot2

How could I calculate the Y-value of curve maximum?

Cheers

Upvotes: 0

Views: 980

Answers (1)

IRTFM
IRTFM

Reputation: 263362

It would seem to me that code changes of "x" to "y" and 'vline' to 'hline' and "xintercept" to "yintercept" would be all that were needed:

gb <- ggplot_build(p1)

exact_y_value_of_the_curve_maximum <- gb$data[[1]]$y[which(diff(sign(diff(gb$data[[1]]$y)))==-2)+1]

p1 + geom_hline( yintercept =exact_y_value_of_the_curve_maximum)

exact_y_value_of_the_curve_maximum

I don't think I would call these "exact" since they are only numerical estimates. The other way to get that value would be 

max(gb$data[[1]]$y)

As the $data element of that build-object can be examined:

> str(gb$data)
List of 2
 $ :'data.frame':   80 obs. of  7 variables:
  ..$ x    : num [1:80] 1 1.19 1.38 1.57 1.76 ...
  ..$ y    : num [1:80] -123.3 -116.6 -109.9 -103.3 -96.6 ...
  ..$ ymin : num [1:80] -187 -177 -166 -156 -146 ...
  ..$ ymax : num [1:80] -59.4 -56.5 -53.5 -50.3 -46.9 ...
  ..$ se   : num [1:80] 29.3 27.6 25.9 24.3 22.8 ...
  ..$ PANEL: int [1:80] 1 1 1 1 1 1 1 1 1 1 ...
  ..$ group: int [1:80] 1 1 1 1 1 1 1 1 1 1 ...
 $ :'data.frame':   16 obs. of  4 variables:
  ..$ x    : num [1:16] 1 2 3 4 5 6 7 8 9 10 ...
  ..$ y    : num [1:16] -79.6 -84.7 -88.4 -74.1 -29.6 ...
  ..$ PANEL: int [1:16] 1 1 1 1 1 1 1 1 1 1 ...
  ..$ group: int [1:16] 1 1 1 1 1 1 1 1 1 1 ...

Upvotes: 3

Related Questions