What is "partial matching"?
Partial matching explained
R has a very useful functionality called "partial matching," where we can
match a incomplete character string or variable name with a list of options.
This is achieved using the base-R function pmatch(), but many R functions make use of it,
as do many humdrumR functions.
For example, let's say we have a data.frame (let's call it df) with three columns: "Number", "Letter", and "Date":
df <- data.frame(Number = 1:2, Letter = c('A', 'B'), Date = c("January", "February"))If I want to access the Number column, most programming languages would require I write at very least df$Number.
However, R will give me the correct field even if I write df$Numb, df$Num, or even df$N.
This is partial matching!
The matching happens left-to-right, so as long as I get the beginning of variable right, it will work.
Of course, partial matching only works up to the point that the string matches unambiguously.
For example, if added a Dare column to df, then df$D or df$Da would return NULL because they are ambiguous.
You'd need to write at least Dar or Dat to get the Dare and Date columns respectively.
See also
Other R lessons.:
evaluatingExpressions,
groupingFactors,
recycling,
vectorization