x_chr <- c("2019", "2019-03-01", "2019-03", "2018", "", "2018", "")
y_chr <- c("2019", "2019-03", "2019-03-01", "2016-05", "2018", "", "")
x <- as.parttime(x_chr)
y <- as.parttime(y_chr)
includes(x, y)
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