distDD: keep every bin in the table when one is dropped

R/didFF.R

@@ -514,10 +514,14 @@ didFF <-function(
       att   = att
     )
   } else {
+    # Sigmahat only covers the bins kept above; a dropped bin has no
+    # standard error to report.
+    test_se <- base::rep(NA_real_, base::length(point_estimates))
+    test_se[keep_IF] <- base::sqrt(base::diag(Sigmahat))
     implied_dist_table <- base::data.frame(
       level          = bin2,
       test.estimates = point_estimates,
-      test.se        = base::sqrt(base::diag(Sigmahat))
+      test.se        = test_se
     )
 
     didFF_out <- base::list(

tests/test_distDD.R

@@ -0,0 +1,38 @@
+library(testthat)
+library(didFF)
+
+#-----------------------------------------------------------------------------
+# distDD keeps every bin in its table when one of them is dropped from the
+# covariance for having a degenerate influence function.
+data(mpdta, package = "did")
+
+run_distDD <- function(...) {
+  suppressWarnings(
+    distDD(
+      data          = mpdta,
+      yname         = "lemp",
+      tname         = "year",
+      idname        = "countyreal",
+      gname         = "first.treat",
+      control_group = "nevertreated",
+      nbins         = 6,
+      seed          = 0,
+      aggte_type    = "dynamic",
+      ...
+    )
+  )
+}
+
+test_that("distDD returns one row per bin when a bin is dropped", {
+  full    <- run_distDD()
+  dropped <- run_distDD(balance_e = 1)
+
+  expect_equal(NROW(full$table), 6)
+  expect_false(anyNA(full$table$test.se))
+
+  expect_equal(NROW(dropped$table), 6)
+  expect_equal(as.character(dropped$table$level), as.character(full$table$level))
+  expect_equal(sum(is.na(dropped$table$test.se)), 1)
+  expect_true(all(dropped$table$test.se[!is.na(dropped$table$test.se)] > 0))
+  expect_false(anyNA(dropped$table$test.estimates))
+})