Get nearest low and high values across multiple dataframe columns

Question

I have a dataframe similar to this:

import pandas as pd

id = [1001, 1002, 1003]
a = [156, 224, 67]             
b = [131, 203, 61]          
c = [97, 165, 54]        
d = [68, 122, 50]
value = [71, 180, 66]

df = pd.DataFrame({'id':id, 'a':a, 'b':b, 'c':c, 'd':d, 'value':value})

id	a	b	c	d	value
1001	156	131	97	68	71
1002	224	203	165	122	180
1003	67	61	54	50	66

For each row, I would like to evaluate columns a-d and within them identify the next lowest and next highest values, as compared to value. So in this example, the expected result would look like:

id	a	b	c	d	value	nxt_low	nxt_high
1001	156	131	97	68	71	68	97
1002	224	203	165	122	180	165	203
1003	67	61	54	50	66	61	67

I have tried creating a single column with a numpy array from a-d and trying to do some operations that way, but I’m not applying it correctly and have been unable to get the desired result. Any help is greatly appreciated.

Asked By: wsilva916

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Source

Answer 1

you can get nearest low following code:

df.apply(lambda x: x[x < x[-1]].max(), axis=1)

output:

0     68
1    165
2     61
dtype: int64

get nearest low and high and make result to columns:

df[['nxt_low', 'nxt_high']] = df.apply(lambda x: [x[x < x[-1]].max(), x[x > x[-1]].min()], axis=1, result_type='expand')

df:

    id      a   b   c   d   value   nxt_low nxt_high
0   1001    156 131 97  68  71      68      97
1   1002    224 203 165 122 180     165     203
2   1003    67  61  54  50  66      61      67

If id is nearest low or high, modify code a bit.

df[['nxt_low', 'nxt_high']] = df.iloc[:, 1:].apply(lambda x: [x[x < x[-1]].max(), x[x > x[-1]].min()], axis=1, result_type='expand')

Answered By: Panda Kim

Answer 2

Here is a way:

cols = ['a','b','c','d']
df2 = df[cols].sub(df['value'],axis=0)
df = (df.assign(nxt_low = df.where(df2.lt(0)).max(axis=1),
nxt_high = df.where(df2.gt(0)).min(axis=1)))

Output:

     id    a    b    c    d  value  nxt_low  nxt_high
0  1001  156  131   97   68     71     68.0      97.0
1  1002  224  203  165  122    180    165.0     203.0
2  1003   67   61   54   50     66     61.0      67.0

Answered By: rhug123

Get nearest low and high values across multiple dataframe columns

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