I need to do a matching on data to have it balanced for the two groups defined by a variable according to certain variables. I want to do a 1:2 matching.
I used this code a few months ago and it returned what I needed.
Today I tried to run it again but the outcome was not the same and I think there is a bug.
When I display the dataset post matching I have the subclass variable which should tell me each case which 2 controls it has been matched to. But this doesn’t work well today: I see 2 records for each subclass value (1 case and 1 control) until the last subclass for which I see 1 case and lots of controls. The total records are 3 times the number of cases to be matched but the subclasses are not correct and I cannot verify each case to which 2 controls it has been matched.

Actual versions:

R version 4.4.2 (2024-10-31 ucrt)

MatchIt version: 4.6.0

This is the code:

library(MatchIt)
library(writexl)

data("lalonde")
m.out2<-matchit(treat ~ age+educ+married+race,data = lalonde, method = "nearest",
distance = "mahalanobis", exact = c("race"), caliper = c(age = 5), std.caliper = FALSE,ratio = 2, random = TRUE)

m.data2 <- match.data(m.out2)

write_xlsx(m.data2, "m.data2.xlsx")