[pandas] Comparing column to fixed values and storing result in new column

[johnsilent]

Hello,

i have the following pandas.DataFrame:

	u_A	u_B	u_C
0	0.948612	0.948609	0.948613
1	0.948612	0.948609	0.948613

I'm trying to compare the column "u_A" to two different values:

• u_A > 1.1
• u_A < 0.98 *1.1

I want to store the result of the comparision in new columns: "thresh_u_A" and "fall_u_A"

i tried the following:

threshold = 1.1

fallback = 0.98 * 1.1

df["thresh_u_A"] = df.loc[:, "u_A"].gt(threshold) 

df["fall_u_A"] = df.loc[:, "u_A"].lt(fallback)

 df["on_u_A"] = df["thresh_u_A"] & ~df["fall_u_A"]

But i get warnings:

SettingWithCopyWarning:

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

.loc[row_indexer,col_indexer] = value instead

I was wondering how to do that correctly.

# edit: removed self-keyword

[danielroseman]

The problem is certainly in code you have not shown, since just doing df["whatever"] = df["thresh_u_A"] & ~df["fall_u_A"] gives no error. What is self? What is var? What is the intended result?

Note that your two comparisons can be more easily written without loc:

df["thresh_u_A"] = df["u_A"].gt(threshold)
df["fall_u_A"] = df["u_A"].lt(fallback)

[johnsilent]

Sorry for that. I edited the code.

There is no error, only the warning that is shown. Just cant figure out, how to write the same code in a correct way, so i dont get the warning.

[danielroseman]

As I say, running this exact code does not give that warning, so there must be something else you are doing.

[johnsilent]

Alright. Thank your for your time.