select string array values based on another array

Question

I can select data that is equal to a value with

data = rand(1:3, 10)
value = 2
data .== value

or equal to a list of values with

values = [1, 2]
in.(data, (values,))

The last one is generic and also works for a scalar: in.(data, (value, )) .

However, this works for Int, but the generic does not work for String values:

data = rand(["A", "B", "C"], 10)
value = "B"
data .== value
values = ["A","B"]
in.(data, (values, ))
in.(data, (value, ))
ERROR: use occursin(x, y) for string containment

Is there a generic way for Strings?

For a generic val input I'm now writing the following, but I feel there must be a better solution.

isa(val, AbstractArray) ? in.(data, (val,)) : data .== val

Background: I'm creating a function to select rows from a dataframe (and do something with them) but I want to allow for both a list of values as well as a single value.

Bogumił Kamiński · Accepted Answer · 2018-11-16 14:35:44Z

2

Here is a trick that is worth knowing:

[x;]

Now - if x is an array it will remain an array. If x is a scalar it will become a 1-element array. And this is exactly what you need.

So you can write

in.(data, ([val;],))

The drawback is that it allocates a new array, but I guess that val is small and it is not used in performance critical code? If the code is performance critical I think it is better to treat scalars and arrays by separate branches.

answered Nov 16, 2018 at 14:35

Bogumił Kamiński

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