86899

R - Fitting a model per subject using data.table or dplyr

Question:

I have a set of observations for many subjects and I would like to fit a model for each subject.

I"m using the packages data.table and fitdistrplus, but could also try to use dlpyr.

Say my data are of this form:

#subject_id #observation 1 35 1 38 2 44 2 49

Here's what I've tried so far:

subject_models <- dt[,fitdist(observation, "norm", method = "mme"), by=subject_id]

This causes an error I think because the call to fitdist returns a fitdist object which is not possible to store in a datatable/dataframe.

Is there any intuitive way to do this using data.table or dplyr?

<strong>EDIT:</strong> A dplyr answer was provided, but I would appreciate a data.table one as well, I'll try to run some benchmarks against the two.

Answer1:

This can be easily achieved with the purrr package

I assume its the same thing @alistaire suggested

library(purrr) library(dplyr) library(fitdistrplus) dt %>% split(dt$subject_id) %>% map( ~ fitdist(.$observation, "norm", method = "mme"))

Alternatively, without purrr,

dt %>% split(dt$subject_id) %>% lapply(., function(x) fitdist(x$observation, "norm", method = "mme"))

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