uniquePresent function

Extract unique non-missing value from vector

uniquePresent(x, req.n1 = TRUE, na.pattern)

Arguments

• x: A vector, either numeric or character.
• req.n1: Require one unique value? If TRUE (default), an error is thrown if non-unique values found. If FALSE, all the unique values are returned.
• na.pattern: In addition to NA-elements, what text strings should be considered missing? Default is empty strings and strings only containing white spaces (na.pattern="^ *$").

Returns

a vector of same class as x

Details

This function is particularly useful when combining data sets of which only some contain certain variables. uniquePresent with req.n1=TRUE makes sure the result is a single unique value (e.g., within subjects). A typical use is carrying subject-level covariates from one data set to another in a longitudinal analysis.