Run several SFA models by a group and store the output in a list

I am running a Stochastic Frontier model (using the package frontier) by the group industry as follows:

1. data is a panel data frame with index year and individual id and columns as below:
2. Columns: y1, x1, x2and x3 are all numerical variables. industry is a character variable.

library(dplyr)
library(frontier)
sfa_out <- data %>%
  group_by(industry) %>%
  do(
    mod <- sfa(log(y1) ~ log(x1) + log(x2) + log(x3),
               ineffDecrease = T,
               truncNorm = F,
               timeEffect = T,
               data = .))

I want mod to store the output of the industry-group SFA estimated models. I don't think SFA-specific knowledge is required here. Thanks.

This did the trick:

library(dplyr)
library(frontier)
library(plm)

sfa_out <- data %>%
  group_by(industry) %>%
  do(
    mod = sfa(log(y1) ~ log(x1) + log(x2) + log(x3),
               ineffDecrease = T,
               truncNorm = F,
               timeEffect = T,
               data = pdata.frame(., index = c("individual id", "year"))))

To then display each model you could do this:

# to display all industry models 
sfa_out$mod
# to display specific industry model
sfa$mod[[1]]
sfa$mod[[2]]
.
.
.
sfa$mod[[n]]
# to get the estimated efficiency measure for nth model in sfa_out$mod
efficiencies(sfa_out$mod$[[n]])