Add warning if a variable name is repeated twice in match.on argument

ChristopherLucas / MatchingFrontier

Optimal pruning for imbalance minimization in causal inference

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Add warning if a variable name is repeated twice in match.on argument #34

Open nielsenrich opened 4 years ago

nielsenrich commented 4 years ago

Roozbeh included the same variable twice in a long list of matching variables and got this unhelpful error message: Calculating Mahalanobis distances... Error in solve.default(cov(dataset[, matchVars])) : Lapack routine dgesv: system is exactly singular: U[18,18] = 0