dataframe - 加入多个数据帧

Question

我想知道 Julia DataFrames 是否有办法一次性加入多个数据帧，

 using DataFrames

 employer = DataFrame(
    ID = Array{Int64}([01,02,03,04,05,09,11,20]),
    name = Array{String}(["Matthews","Daniella", "Kofi", "Vladmir", "Jean", "James", "Ayo", "Bill"])
    )

salary = DataFrame(
    ID = Array{Int64}([01,02,03,04,05,06,08,23]),
    amount = Array{Int64}([2050,3000,3500,3500,2500,3400,2700,4500])
)

hours = DataFrame(
    ID = Array{Int64}([01,02,03,04,05,08,09,23]),
    time = Array{Int64}([40,40,40,40,40,38,45,50])
)

# I tried adding them in an array but ofcoures that results in an error
empSalHrs = innerjoin([employer,salary,hours], on = :ID)

# In python you can achieve this using
import pandas as pd 
from functools import reduce

df = reduce(lambda l,r : pd.merge(l,r, on = "ID"), [employer, salary, hours])

在 julia 中是否有类似的方法可以做到这一点？

Answer 1

你快到了。正如 DataFrames.jl manual 中所写的那样你只需要传递一个以上的数据帧作为参数。

using DataFrames

 employer = DataFrame(
    ID = [01,02,03,04,05,09,11,20],
    name = ["Matthews","Daniella", "Kofi", "Vladmir", "Jean", "James", "Ayo", "Bill"])
    

salary = DataFrame(
    ID = [01,02,03,04,05,06,08,23],
    amount = [2050,3000,3500,3500,2500,3400,2700,4500])


hours = DataFrame(
    ID = [01,02,03,04,05,08,09,23],
    time = [40,40,40,40,40,38,45,50]
)

empSalHrs = innerjoin(employer,salary,hours, on = :ID)

如果出于某种原因您需要将数据帧放入 Vector ，您可以使用拆分来实现相同的结果

empSalHrs = innerjoin([employer,salary,hours]..., on = :ID)

另外，请注意，我稍微更改了数据框的定义。自 Array{Int}是一种抽象类型，不应该用于变量声明，因为它不利于性能。在这种特殊情况下，这可能并不重要，但最好从一开始就养成良好的习惯。而不是 Array{Int}一个可以使用

Array{Int, 1}([1, 2, 3, 4])

Vector{Int}([1, 2, 3, 4])

Int[1, 2, 3]

[1, 2, 3]

最后一个是合法的，因为在这个简单的场景中，Julia 可以自己推断容器的类型。