如何使用 join() 连接具有多个键的两个 DataFrame

Question

尝试使用 join() 命令而不是合并来学习此代码 尝试过left.set_index('key1','key2').join(right.set_index('key1','key2'))但这不起作用

left = pd.DataFrame(
{
    "key1": ["K0", "K0", "K1", "K2"],
    "key2": ["K0", "K1", "K0", "K1"],
    "A": ["A0", "A1", "A2", "A3"],
    "B": ["B0", "B1", "B2", "B3"],
})


right = pd.DataFrame(
{
    "key1": ["K0", "K1", "K1", "K2"],
    "key2": ["K0", "K0", "K0", "K0"],
    "C": ["C0", "C1", "C2", "C3"],
    "D": ["D0", "D1", "D2", "D3"],
})
result = pd.merge(left, right, on=["key1", "key2"])

Answer 1

您需要一个方括号来指定多个键。 请使用['key1', 'key2']代替'key1','key2' 。 将中间 df 放入单独的变量以避免混淆是明智的，例如left_k1k2 = left.set_index(['key1', 'key2'])然后执行left_k1k2.join(right_k1k2) 。

left.set_index(['key1', 'key2']).join(right.set_index(['key1', 'key2'])) # LJR
right.set_index(['key1', 'key2']).join(left.set_index(['key1', 'key2'])) # RJL

# LJR
|              | A   | B   | C   | D   |
|:-------------|:----|:----|:----|:----|
| ('K0', 'K0') | A0  | B0  | C0  | D0  |
| ('K0', 'K1') | A1  | B1  | nan | nan |
| ('K1', 'K0') | A2  | B2  | C1  | D1  |
| ('K1', 'K0') | A2  | B2  | C2  | D2  |
| ('K2', 'K1') | A3  | B3  | nan | nan |