R help - Mar 2019 - help with sitar growth model

I want to obtain the individual biological parameters (ie age at takeoff,
final height velocity at takeoff) after a sitar model. (I do understand a
sitar model fits a mean curve for the population).

I have managed to obtain the parameters for one individual using the code
below,

      library(sitar)
      data(heights)
      library(tidyverse)

      m1 <- sitar(x=age, y=height, id=id, data=heights, df=5)

      #velocity at takeoff for individual 1

     (vel_attoff<-getPeakTrough(plot_v(m1, subset=age < 14 &id==1) ,
peak=FALSE))

What I want is to produce a dataframe with the id and the velocity at
takeoff for each individual in the dataset.
I have tried to do this

      for (i in seq_along(heights[1])){
       print(getPeakTrough(plot_v(m1, subset=age < 14 & id==i) ,
peak=FALSE))
        }

But it prints only one x and y  value

Any assistance will be greatly appreciated

-- 
R T CHIRUKA
University of Fort Hare
Statistics Department
Box X 1314
Alice
5700
South Africa

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