Python 替换熊猫数据框中大于数字的值
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Replacing values greater than a number in pandas dataframe
提问by Zanam
I have a large dataframe which looks as:
我有一个大数据框，它看起来像：
df1['A'].ix[1:3]
2017-01-01 02:00:00 [33, 34, 39]
2017-01-01 03:00:00 [3, 43, 9]
I want to replace each element greater than 9 with 11.
我想用 11 替换大于 9 的每个元素。
So, the desired output for above example is:
因此，上述示例所需的输出是：
df1['A'].ix[1:3]
2017-01-01 02:00:00 [11, 11, 11]
2017-01-01 03:00:00 [3, 11, 9]
Edit:
编辑：
My actual dataframe has about 20,000 rows and each row has list of size 2000.
我的实际数据框有大约 20,000 行，每行都有大小为 2000 的列表。
Is there a way to use numpy.minimumfunction for each row? I assume that it will be faster than list comprehensionmethod?
有没有办法numpy.minimum为每一行使用函数？我认为它会比list comprehension方法更快？
采纳答案by jezrael
You can use applywith list comprehension:
你可以用apply与list comprehension：
df1['A'] = df1['A'].apply(lambda x: [y if y <= 9 else 11 for y in x])
print (df1)
A
2017-01-01 02:00:00 [11, 11, 11]
2017-01-01 03:00:00 [3, 11, 9]
Faster solution is first convert to numpy arrayand then use numpy.where:
更快的解决方案是首先转换为numpy array然后使用numpy.where：
a = np.array(df1['A'].values.tolist())
print (a)
[[33 34 39]
[ 3 43 9]]
df1['A'] = np.where(a > 9, 11, a).tolist()
print (df1)
A
2017-01-01 02:00:00 [11, 11, 11]
2017-01-01 03:00:00 [3, 11, 9]
回答by Edouard Cuny
Very simply : df[df > 9] = 11
很简单： df[df > 9] = 11
回答by D.Griffiths
You can use numpy indexing, accessed through the .valuesfunction.
您可以使用 numpy 索引，通过.values函数访问。
df['col'].values[df['col'].values > x] = y
df['col'].values[df['col'].values > x] = y
where you are replacing any value greater than x with the value of y.
用 y 的值替换任何大于 x 的值。
So for the example in the question:
因此，对于问题中的示例：
df1['A'].values[df1['A'] > 9] = 11
df1['A'].values[df1['A'] > 9] = 11
回答by CFW
I came for a solution to replacing each element larger than h by 1 else 0, which has the simple solution:
我来找一个解决方案，用 1 else 0 替换每个大于 h 的元素，它有一个简单的解决方案：
df = (df > h) * 1
(This does not solve the OP's question as all df <= h are replaced by 0.)
（这不能解决 OP 的问题，因为所有 df <= h 都被 0 替换。）
