dataframe value comparison in python

Question

Team, I have a huge pandas data frame of historical stock OHLC data. I want to compare a particular column value , for e.g. I want to compare today's open with yesterdays open or today's low with yesterdays low ( I have almost 5000 rows to compare )

I tried something like followed, but it gives me just one constant value..

#calculate Low Travel point
df['1back'] = df['low'].iloc[-1]

any suggestion plese??

Rikki · Accepted Answer · 2021-02-26 03:53:57Z

2

This code:

import pandas as pd


df = pd.DataFrame([
    [10, 102],
    [12, 98],
    [13, 99],
    [15, 94]
],
    columns=['p1', 'p2']
)

print(df.head(10))

df['p1_diff'] = df['p1'].diff(1)
df['p2_diff'] = df['p2'].diff(1)

print(df.head(10))

Should provide the following output:

   p1   p2
0  10  102
1  12   98
2  13   99
3  15   94
   p1   p2  p1_diff  p2_diff
0  10  102      NaN      NaN
1  12   98      2.0     -4.0
2  13   99      1.0      1.0
3  15   94      2.0     -5.0

Process finished with exit code 0

What you look for is diff. Reference here.

answered Feb 26, 2021 at 3:53

Rikki

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2 Comments

Dharmesh Over a year ago

Thanks Rikki! This solves half of my problem. I also need to print the value also... to be clear like this .... p1 p2 0 10 102 1 12 98 2 13 99 3 15 94 p1 p2 p1_last p2_last 0 10 102 NaN NaN 1 12 98 10 102 2 13 99 12 98 3 15 94 13 99

Dharmesh Over a year ago

Thanks Rikki! I checked the link you mentioned in reference. The SHIFT works like a charm!!... Thank you very much...

Dharmesh · Accepted Answer · 2021-03-05 03:34:00Z

0

calculate EMA/SMA togllers

filter_EMA_TOGGLER_Steady = df['EMA_CROSS'] ==  df['EMA_CROSS'].shift(-1)
filter_EMA_TOGGLER_BUY = (df['EMA_CROSS'] == 'SELL') &  (df['EMA_CROSS'].shift(-1) == 'BUY')
filter_EMA_TOGGLER_SELL = (df['EMA_CROSS'] == 'BUY') &  (df['EMA_CROSS'].shift(-1) == 'SELL')
#SMA 
filter_SMA_TOGGLER_Steady = df['SMA_CROSS'] ==  df['SMA_CROSS'].shift(-1)
filter_SMA_TOGGLER_BUY = (df['SMA_CROSS'] == 'SELL') &  (df['SMA_CROSS'].shift(-1) == 'BUY')
filter_SMA_TOGGLER_SELL = (df['SMA_CROSS'] == 'BUY') &  (df['SMA_CROSS'].shift(-1) == 'SELL')

answered Mar 5, 2021 at 3:34

Dharmesh

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1 Comment

smci Over a year ago

Please put a data snippet in the question, otherwise it isn't reproducible (minimal reproducible example) and how could anyone other than you answer it?

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