Adding has_key() and/or default values to hasmaps

[vgherard]

Hi! I just came along this very nice package and was trying to play around a bit with hash tables.

My particular use cases require many queries to keys which may be absent from the table. For a simplified example, suppose I want to build a table of occurrences of elements in a vector v of strings through a single pass over the vector; ideally, I would like to do something like this:

# pseudocode
h <- hashmap("integer")
for (x in v) {
    h[x] <- h[x] + 1
}

where, if x is not yet a key, h[x] on the right-hand side of the assignment should return zero (like e.g. a C++ STL map with numeric values).

As far as I can see, the only sensible way to correctly implement my pseudocode above is to wrap the h[x]<- assignment in a tryCatch() clause. It would be thus nice to have either:

• an has_key() method to check the presence of x in keys(h) in constant time, or
• the possibility to set a default (R object) value to missing keys.

If you think any of these two features are worth implementing, I could try to provide some starting code!

Hope this helps,
Thanks.

Valerio