每次列中的字符串值更改时如何拆分数据框？

Question

I've got a dataframe of the form:

         time     value   label
0  2020-01-01 -0.556014    high
1  2020-01-02  0.185451    high
2  2020-01-03 -0.401111  medium
3  2020-01-04  0.436111  medium
4  2020-01-05  0.412933    high
5  2020-01-06  0.636421    high
6  2020-01-07  1.168237    high
7  2020-01-08  1.205073    high
8  2020-01-09  0.798674    high
9  2020-01-10  0.174116    high

And I'd like to populate a list of dataframes where each dataframe is built when the string in the column label changes. So the first dataframe would be:

         time     value   label
0  2020-01-01 -0.556014    high
1  2020-01-02  0.185451    high

The second dataframe would be:

         time     value   label
2  2020-01-03 -0.401111  medium
3  2020-01-04  0.436111  medium

And so on. And the desired list would be [df, df, ...] . If you think that a dict would be a more appropriate container I wouldn't mind that at all.

There's a similar post named split data frame pandas if sequence of column value change , but that only handles changes in numeric values. I've made a few attempts but keep running into indexing problems when comparing a row value for label with the previous value. So any suggestions would be great!

Here's a reproducible snippet:

# imports
import plotly.express as px
import plotly.graph_objects as go
import pandas as pd
import numpy as np
import random

# settings
observations = 100
np.random.seed(5)
value = np.random.uniform(low=-1, high=1, size=observations).tolist()
time = [t for t in pd.date_range('2020', freq='D', periods=observations).format()]

df=pd.DataFrame({'time': time, 
                 'value':value})
df['value']=df['value'].cumsum()

def classify(e):
    if e > 0.75: return 'high'
    if e > 0.25: return 'medium'
    if e >= 0: return 'low'

df['label1'] = [(elem-df['value'].min())/(df['value'].max()-df['value'].min()) for elem in df['value']]
df['label'] = [classify(elem) for elem in df['label1']]
df = df.drop('label1', 1)
df

Answer 1

I would create a column that increments on each change, then group by that column. If you need separate dataframes you can assign them in a loop.

df['group'] = df['label'].ne(df['label'].shift()).cumsum()
df = df.groupby('group')
dfs = []
for name, data in df:
    dfs.append(data)

dfs will be a list of dataframes like so:

[         time     value label  group
 0  2020-01-01 -0.556014  high      1
 1  2020-01-02  0.185451  high      1,
          time     value   label  group
 2  2020-01-03 -0.401111  medium      2
 3  2020-01-04  0.436111  medium      2,
          time     value label  group
 4  2020-01-05  0.412933  high      3
 5  2020-01-06  0.636421  high      3
 6  2020-01-07  1.168237  high      3
 7  2020-01-08  1.205073  high      3
 8  2020-01-09  0.798674  high      3
 9  2020-01-10  0.174116  high      3]