Python(Pandas)错误'标签[阿尔及利亚]不在[索引]中

Question

我不明白为什么会这样

df[(df['Gold']>0) & (df['Gold.1']>0)].loc[((df['Gold'] - df['Gold.1'])/(df['Gold'])).abs().idxmax()]

但是当我分开时(df['Gold'] + df['Gold.1'] + df['Gold.2']) 它停止工作给我错误,你可以在下面找到.

有趣的是,以下行有效

df.loc[((df['Gold'] - df['Gold.1'])/(df['Gold'] + df['Gold.1'] + df['Gold.2'])).abs().idxmax()]

我不明白自从我开始学习Python和Pandas以来发生了什么.我需要了解发生这种情况的原因以及如何解决这个问题.

错误

KeyError:'标签[阿尔及利亚]不在[索引]中

DataFrame snap

Answer 1

你的问题是boolean indexing:

df[(df['Gold']>0) & (df['Gold.1']>0)]

返回一个过滤后的DataFrame,它不包含您使用此值计算index的max值Series:

((df['Gold'] - df['Gold.1'])/(df['Gold'] + df['Gold.1'] + df['Gold.2'])).abs().idxmax()

在你的数据中Algeria.

所以loc逻辑上抛出一个KeyError.

一个可能的解决办法是赋予新的过滤DataFrame来df1,然后得到相应的最大值的指数Series使用idxmax:

df1 = df[(df['Gold']>0) & (df['Gold.1']>0)]
df2 = df1.loc[((df1['Gold']-df1['Gold.1'])/(df1['Gold']+df1['Gold.1']+df1['Gold.2'])).abs().idxmax()]