Python Forum

Hello,

this is my first post about Python, and also this is my first post in English. So... thank you for your patience :)... And sorry for my low english level, I'm practicing to improve.

I want to build a pandas Dataframe but the rows info are coming to me one by one (in a for loop), in form of a dictionary (or json).

In each iteration I receive a dictionary where the keys refer to the columns, and the values are the rows values. For example:

1st Iteration I receive:
d_val = {'key1': 1.1, 'key2':2.2, 'key3':3.3}

And I want to build a dataframe (called df), where column names will be d_val.keys(), and the first row values will be d_val.values()

2nd Iteration I receive:
{'key1': 4.4, 'key2':5.5, 'key3': 6.6}

And I want to append the values to a new row in the datframe.

Example outcome wanted:

key1---key2----key3
1.1-----2.2------3.3
4.4-----5.5------6.6

And each new iteration, will make a new row append. I will be sure that in each iteration the dict keys are the same.

I try to create a empty dataframe or a dataframe with only de columns values, and then use the DataFrame.append method... but never works. I'm lost, because I think that It will not be so difficult.

I hope that I have explained well.

Thanks

Example below should help you...

import pandas as pd

df = pd.DataFrame({'key1': [], 'key2': [], 'key3': []})
for i in range(10):
    df = df.append({'key1': i, 'key2': i*2, 'key3': i**3}, ignore_index=True)

Hello scidam,

I've adapted it to my program and it works! Thank you.

But in my first message I have simplified the problem a little... ;) I was afraid of not explaining myself well and that's why I simplified it...

Really, I need to do this, but I don't know how many items will have the dict a priori. Then, I don't know if I will have 'key1', 'key2'... 'keyn'

In each iteration, I will receive a message with the information. When I receive the first message (in the first iteration), then I analize the message and I see the dict/json items. Before that, I don't know how many columns will have the dataframe.

Is there a more generic way?

Thanks

Pandas is quite smart. Don't worry about new keys, you can even start with an empty data frame, e.g.

import pandas as pd
import random
df = pd.DataFrame()
for j in range(10):
    df = df.append({'key_%s'%random.choice('abcde'): j}, ignore_index=True)

Output:
>>> df
   key_d  key_b  key_e  key_c
0    0.0    NaN    NaN    NaN
1    1.0    NaN    NaN    NaN
2    2.0    NaN    NaN    NaN
3    NaN    3.0    NaN    NaN
4    NaN    NaN    4.0    NaN
5    5.0    NaN    NaN    NaN
6    6.0    NaN    NaN    NaN
7    NaN    NaN    7.0    NaN
8    NaN    NaN    NaN    8.0
9    NaN    NaN    NaN    9.0

Hello scidam,

great! Thank you!