check.unique: Check whether a data set identifier occurs only once for each...
In mnel/linkedEpi: Tools for linked data analysis

Description Usage Arguments Value Examples

This function will check if a identifier within a data.frame is unique. This is used, for example, to ensure that merges are performed on a one-to-one or one-to-many basis and not a many-to-many basis that might cause problems

1	check.unique(data, id = "ppn")

`data`	data frame to check
`id`	character string of length 1 defining the column which contains the unique identifer

logical TRUE if unique, FALSE if not.

df.non <- data.frame(ppn = c(1L,1L,2L), var1 = seq_len(3))
df.unique <- data.frame(ppn = seq_len(3), var2 = seq_len(3))
check.unique(df.non, id = 'ppn')
check.unique(df.unique, id = 'ppn')