How can we deal with error message that is "duplicate couples (id-time)..." ?

[korkut_keles]

When I run the following code (fixed effect regression):

total_index_dem_model <- plm(SupDem ~ distance + gdpcap + pop + dem_duration + aut_neighbours
                          ,data = df_a,
                          index = c("country", "year"),
                          model = "within",
                          effect="twoways")
summary(total_index_dem_model)

I get the following error:

  0 (non-NA) cases
In addition: Warning message:
In pdata.frame(data, index) :
  duplicate couples (id-time) in resulting pdata.frame
 to find out which, use, e.g., table(index(your_pdataframe), useNA = "ifany")

I could not solve the problem. WHen I run the suggested code in the warning message nothing changes. Many thanks in advance.

[andresrcs]

To help us help you, could you please prepare a reproducible example (reprex) illustrating your issue? Please have a look at this guide, to see how to create one:

FAQ: How to do a minimal reproducible example ( reprex ) for beginners

A minimal reproducible example consists of the following items: A minimal dataset, necessary to reproduce the issue The minimal runnable code necessary to reproduce the issue, which can be run on the given dataset, and including the necessary information on the used packages. Let's quickly go over each one of these with examples: Minimal Dataset (Sample Data) You need to provide a data frame that is small enough to be (reasonably) pasted on a post, but big enough to reproduce your issue. Let's say, as an example, that you are working with the iris data frame head(iris) #> Sepal.Length Sepal.Width Petal.Length Petal.Width Species #> 1 5.1 3.5 1.4 0.…