Good morning,
I´m currently trying to run a truncated regression loop on my dataset. In the following I will give you a reproducible example of my dataframe.
library(plyr)
library(truncreg)
df <- data.frame("grid_id" = rep(c(1,2), 6),
"htcm" = rep(c(160,170,175), 4),
stringsAsFactors = FALSE)
View(df)
Now I tried to run a truncated regression on the variable "htcm" grouped by grid_id to receive only coefficients (intercept such as sigma), which I then stored into a dataframe. This code is written based on the ideas of @hadley
reg <- dlply(df, "grid_id", function(.)
truncreg(htcm ~ 1, data = ., point = 160, direction = "left")
)
regcoef <- ldply(reg, coef)
As this code works for one of my three datasets, I receive error messages for the other two ones. The datasets do not differ in any column but in their absolute length (length(df1) = 4,000; length(df2) = 100,000; length(df3) = 13,000)
The error message which occurs is
"Error in array(x, c(length(x), 1L), if (!is.null(names(x))) list(names(x), : 'data' must be of type vector, was 'NULL'
I do not even know how to reproduce an example where this error code occurs, because this code works totally fine with one of my three datasets. I already accounted for missing values in both columns.
Does anyone has a guess what I can fix to this code?
Thanks!!
EDIT:
I think I found the origin of error in my code, the problem is most likely about that in a truncated regression model, the standard deviation is calculated which automatically implies more than one observation for any group. As there are also groups with only n = 1 observations included, the standard deviation equals zero which causes my code to detect a vector of length = NULL. How can I drop the groups with less than two observations within the regression code?
