使用 np.where 的 for 循环 [英] For loop using np.where

问题描述

我正在尝试在数据框中创建一个新列，用 1 标记驯养的动物.我正在使用 for 循环，但出于某种原因，该循环仅选取 宠物列表.dog、cat 和 gerbil 都应在 domesticated 列下分配为 1.任何人都有解决此问题的方法或更好的方法?

I'm trying to create a new column in a dataframe that labels animals that are domesticated with a 1. I'm using a for loop, but for some reason, the loop only picks up the last item in the pets list. dog, cat, and gerbil should all be assigned a 1 under the domesticated column. Anyone have a fix for this or a better approach?

df = pd.DataFrame(
    {'creature': ['dog', 'cat', 'gerbil', 'mouse', 'donkey']
    })

pets = ['dog', 'cat', 'gerbil']

for pet in pets:
    df['domesticated'] = np.where(df['creature']==pet, 1, 0)

df

推荐答案

您在上次循环迭代中将所有非沙鼠设置为 0.也就是说，当 pet 在上次迭代中为 gerbil 时，所有不等于 gerbil 的条目将对应于 0.这包括 dog 或 cat 条目.您应该一次检查 pets 中的所有值.试试这个:

You are setting all non gerbil to 0 in your last loop iteration. That is, when pet is gerbil in your last iteration, ALL entries that are not equal to gerbil will correspond to 0. This includes entries that are dog or cat. You should check all values in pets at once. Try this:

df['domesticated'] = df['creature'].apply(lambda x: 1 if x in pets else 0)

如果你想坚持使用 np.where:

df['domesticated'] = np.where(df['creature'].isin(pets), 1, 0)

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