lm

This Q & A arises from How to make group_by and lm fast? where OP was trying to do a simple linear regression per group for a large data frame. In theory, a series of group-by regression y ~ x | g is equivalent to a single pooled regression y ~ x * g . The latter is very appealing because statistical test between different groups is straightforward. But in practice doing this larger regression is not computationally easy. My answer on the linked Q & A reviews packages speedlm and glm4 , but pointed out that they can't well address this problem. Large regression problem is difficult,

Does anyone know how to get stargazer to display clustered SEs for lm models? (And the corresponding F-test?) If possible, I'd like to follow an approach similar to computing heteroskedasticity-robust SEs with sandwich and popping them into stargazer as in http://jakeruss.com/cheatsheets/stargazer.html#robust-standard-errors-replicating-statas-robust-option . I'm using lm to get my regression models, and I'm clustering by firm (a factor variable that I'm not including in the regression models). I also have a bunch of NA values, which makes me think multiwayvcov is going to be the best package

I want to do a piecewise linear regression with one break point, where the 2nd half of the regression line has slope = 0 . There are examples of how to do a piecewise linear regression, such as here . The problem I'm having is I'm not clear how to fix the slope of half of the model to be 0. I tried lhs <- function(x) ifelse(x < k, k-x, 0) rhs <- function(x) ifelse(x < k, 0, x-k) fit <- lm(y ~ lhs(x) + rhs(x)) where k is the break point, but the segment on the right is not a flat / horizontal one. I want to constrain the slope of the second segment at 0. I tried: fit <- lm(y ~ x * (x < k) + x *