CODEWITHSUNDEEP
macrosdataframemetaprogrammingjulia
ARM
ARM

Reputation: 1550

How to avoid parsing the contents of strings in a macro

I'm lazy, and got tired of selecting rows in dataframes with code like this (on the 0.4 RC):

using DataFrames
data = DataFrame(num=[1,2,3,4], let=["A", "B", "A", "B"])
subset = data[(data[:num].>1)&(data[:let].=="B"),:]

so I wrote the following macro

# Need to import SubstitutionString from Base
macro sel(dt, conditions) 
    dtstr=string(dt)
    str = string(conditions)
    out_str = replace(str, r":\w+",SubstitutionString(string(dtstr, "[", "\\g<0>", "]"))) 
    out_str = string(dtstr, "[", out_str, ",:]")
    eval(parse(out_str))
end

so that I could instead write 

subset = @sel data (:num.>1)&(:let.=="B")

This works fine, except in the situation where I want to match columns to strings like "Turtles::Leonardo" or "12:25:00". Is there any way to avoid falsely identifying the contents of strings as column names here, or is this a limitation of this sloppy convert-to-string-and-work-on-that metaprogramming?

Upvotes: 2

Views: 68

Answers (2)

mmagnuski
mmagnuski

Reputation: 1275

You could also take a look at DataFramesMeta, where you find a similar macro, which should work in the problematic cases you mention. The macro works this way: 

subset = @where(data, (:num.>1)&(:let.=="B"))

Upvotes: 1

Reza Afzalan
Reza Afzalan

Reputation: 5756

is it helps?

out_str = replace(str, r"(\()(:\w)",SubstitutionString(string(dtstr, "[", "\\g<2>", "]")))

Upvotes: 0

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