Concatenate two columns data into a column in pandas

Question

I have 2 columns in pandas like this:

  column_a       column_b
     ok            pen
     ok            book
    0.615          C/H
    0.551          I/H 

Is there any way to concatenate these 2 columns into a column like this ?:

      column_c
        pen
        book
        0.615
        0.551

I've tried so many ways but it can't give me the desired result i want,

Answer 1

There is a simple solution:

df = pd.DataFrame({"column_a": ["ok", "ok", 0.615, 0.551], "column_b": ["pen", "book", "C/H", "I/H"]})

# Generate your condition
CONDITION = df["column_a"] == "ok"

#Initilize your new column to the first one.
df.loc[:,"together"] = df["column_a"]

# Add new column with the condition, called together
df.loc[CONDITION, "together"] = df["column_b"]


    column_a    column_b    together
0   ok          pen          pen
1   ok          book         book
2   0.615       C/H          NaN
3   0.551       I/H          NaN

So basically you create a copy of the first column and then you define a condition where you want to update the value. In this case I'm using column_a = "ok".

Answer 2

if you literally only need that, you can do it manually:

df
   column_a column_b
0       ok      pen
1       ok     book
2    0.615      C/H
3    0.551      I/H

df['column_c'] = list(df.iloc[0:2, 1]) + list(df.iloc[2:,0])
df

 column_a column_b column_c
0    ok      pen      pen
1    ok     book     book
2  0.615     C/H    0.615
3  0.551     I/H    0.551