Value is tryin to be set on a copy of a slice from DF

问题

I´m doing some stuff with pandas and python. I have the next code

df = pd.read_csv("Request.csv", keep_default_na=False)
df1 = df.loc[(df["Request Status"] == "Closed")]
df1["Request Close-Down Actual"] = pd.to_datetime(df1["Request Close-Down Actual"], errors = 'coerce' )
df3 = df1.loc[(df1["Request Close-Down Actual"] < '2016-11-01') | (df1["Request Close-Down Actual"].isnull())]        
df3.set_index("Request ID", inplace = True)
df3.to_csv("Request1.csv")

The issue is when i run the code i receive the next issue

A value is trying to be set on a copy of a slice from a DataFrame

df1.loc["Request Close-Down Actual"] = pd.to_datetime(df1["Request Close-Down Actual"], errors = 'coerce' )

Can someone give me a hand with this please. Thanks

回答1:

I test it and for me it works nice.

Problem should be in row above:

df1 = df.loc[(df["Request Status"] == "Closed")]

And solution is copy:

#loc is not necessary
df1 = df[df["Request Status"] == "Closed"].copy()

---

Error show loc - try remove it if need select column:

df1.loc["Request Close-Down Actual"] = pd.to_datetime(df1["Request Close-Down Actual"], errors = 'coerce' )

to:

df1["Request Close-Down Actual"] = pd.to_datetime(df1["Request Close-Down Actual"], errors = 'coerce' )

来源：https://stackoverflow.com/questions/42027229/value-is-tryin-to-be-set-on-a-copy-of-a-slice-from-df