How do I get the column names from a DataFrame object or JuliaDB IndexedTable object? Is this possible?
using JuliaDB
import DataFrames
DF = DataFrames
# CREATES AN EXAMPLE TABLE WITH JULIADB
colnames = [:samples, :A, :B, :C, :D]
primary_key = [:samples]
coltypes = [Int[], Float64[],Float64[],Float64[],Float64[]]
sample_sizes = [100,200,300]
example_values = (1, 0.4, 0.3, 0.2, 0.1)
mytable = table(coltypes..., names=colnames, pkey=primary_key) # initialize empty table
# add some data to table
for i in sample_sizes
example_values = (i, 0.4, 0.3, 0.2, 0.1)
table_params = [(col=>val) for (col,val) in zip(colnames, example_values)]
push!(rows(mytable), (; table_params...)) # add row
mytable = table(mytable, pkey = primary_key, copy = false) # sort rows by primary key
end
mytable = table(unique(mytable), pkey=primary_key) # remove duplicate rows which don't exist
# MAKES A DATAFRAME FROM JULIADB TABLE
df = DF.DataFrame(mytable)
For instance, given the above code, how would you check with a conditional if there's a column :E in either mytable or df, (for the purposes of adding such a column if it doesn't exist yet)?
Ultimately, I'm looking for the Julia equivalent of the following Python code:
if 'E' in df.columns:
# ...
else:
# ...
If df is a data frame you can write:
if "E" in names(df)
...
(in JuliaDB.jl it would be JuliaDB.colnames)
but a faster (in terms of run-time and available for data frames option is:
if hasproperty(df, :E)
...
A bit slower, but useful in other cases is (it also works for JuliaDB.jl but first you have to load Tables.jl and write Tables.columnindex instead):
if columnindex(df, :E) != 0
...
The last example columnindex is probably most complex the way it works is described in its documentation:
help?> columnindex
search: columnindex
Tables.columnindex(table, name::Symbol)
Return the column index (1-based) of a column by name in a table with a
known schema; returns 0 if name doesn't exist in table
────────────────────────────────────────────────────────────────────────────
given names and a Symbol name, compute the index (1-based) of the name in
names