Transcranial Doppler (TCD), first described in 1982 [1], is a noninvasive ultrasound (US) study that involves the use of a low-frequency (â¤2 MHz) transducer probe to insonate the basal cerebral arteries through relatively thin bone windows.
Details. as.character and is.character are generic: you can write methods to handle specific classes of objects, see InternalMethods. Further, for as.character the default method calls as.vector, so dispatch is first on methods for as.character and then for methods for as.vector.
Jason Ford, Bureau of Labor Statistics. ABSTRACT. Character string functions allow a user to manipulate character variables in a variety of ways. Users can create new. variables out of parts of existing character variables, verify the contents of variables, find information within a variable, concatenate variables, and eliminate unnecessary blanks.