pandas 移位的列名

Question

Trying to create lags for pandas columns with column_names

Sample DF Code:

df = pd.DataFrame(np.random.randint(0,10,size=(4,2)))
df.shift(1)

OP:

     0   1
0   NaN NaN
1   9.0 2.0
2   4.0 5.0
3   6.0 0.0

but when I try to create this with column names, i get nan

df1=pd.DataFrame(df.shift(1),columns=["lag"+str(each) for each in df.columns])
df1

OP:

    lag0  lag1
0   NaN   NaN
1   NaN   NaN
2   NaN   NaN
3   NaN   NaN

Any suggestion to rectify this?

Answer 1

Here's another approach:

df = df.shift(1)

l = list(df.columns.astype('str'))
s = 'lag'
cols = [s + i for i in l]
df.columns = cols

---

df
    lag0    lag1
0   NaN     NaN
1   7.0     4.0
2   4.0     8.0
3   0.0     9.0

Answer 2

Problem is there are different columns names, so after created new DataFrame columns names not matched and are created misisng values, it is called index alignmenet.

For prevent it is possible convert values to numpy array:

df1=pd.DataFrame(df.shift(1).to_numpy(),columns=["lag"+str(each) for each in df.columns])
print (df1)
   lag0  lag1
0   NaN   NaN
1   2.0   2.0
2   8.0   3.0
3   6.0   8.0

But simplier is use DataFrame.add_prefix :

df1 = df.shift().add_prefix('lag')
print (df1)
   lag0  lag1
0   NaN   NaN
1   1.0   1.0
2   8.0   3.0
3   0.0   4.0