How to set dictionary values to zero in Julia

Not quite the answer to your question, but it may be interesting for you to consider using Dictionaries.jl package, which provides more convenient means to work with dictionaries than Base Dict.

For example, in Dictionaries.jl notation your question can be solved as follows

using Dictionaries

d = dictionary(['a' => 1, 'b' => 2])

map(zero, d)

The replace function comes to mind. It takes a function as first argument that takes a pair as argument and returns the modified pair:

d_new = replace(kv -> kv[1] => 0, d)

Here, each pair kv from d is replaced by kv[1] => 0, where kv[1] is the key and 0 the new associated value. Note that the mutating variant replace! is also available for in-place replacement.

EDIT: another possibility when the dictionary has to be mutated is:

map!(x->0, values(d))

I found the answer to my own question. As mentioned in the Julia docs, dictionaries can be created using generators. So you can copy the keys of the original Dict and assign all the values to be 0 like so

d_new = Dict(i => 0 for i in keys(d))

See also this forum post.