CODEWITHSUNDEEP
pythonpandasindexingdataframe
Elysire
Elysire

Reputation: 713

Python Pandas : select a range of index

datas = [['RAC1','CD0287',1.52], ['RAC1','CD0695',2.08], ['RAC1','ADN103-1',2.01], ['RAC3','CD0258',1.91], ['RAC3','ADN103-3',1.66], ['RAC8','CD0558',1.32], ['RAC8','ADN103-8',2.89]]
labels = ['Plate', 'Sample', 'LogRatio']
df = pd.DataFrame(data = datas, columns=labels, index=[8, 3, 5, 4, 12, 44, 2])

   Plate    Sample  LogRatio
8   RAC1    CD0287      1.52
3   RAC1    CD0695      2.08
5   RAC1  ADN103-1      2.01
4   RAC3    CD0258      1.91
12  RAC3  ADN103-3      1.66
44  RAC8    CD0558      1.32
2   RAC8  ADN103-8      2.89

I would like to find the logratio value for the sample located n rows after "CD0695" sample using the index. 

n = 2
indexCD0695 = df[df['Sample']=="CD0695"].index.tolist()
print(indexCD0695)
> [3] 
logratio_value = df.iloc[indexCD0695[0]+n]['LogRatio']
> 1.32 #NOT THE RESULT I WOULD LIKE

I don't know how to have a single index and not a list so I just take the 1st element of the list indexCD0695[0], it's not my biggest issue. My real problem is that I obtain the value at the index position 3+2 where as I would like to have the index starting with the location of CD0695 : (I can have it with just df.loc) and have the 2nd row after this starting index : 

4   RAC3    CD0258      1.91

So the logratio value is 1.91

I think I have to mix df.loc[indexCD0695] and df.iloc[n] but I don't know how.

Upvotes: 3

Views: 6691

Answers (2)

akuiper
akuiper

Reputation: 215117

Another option is to shift your LogRatio column by n before extracting the value:

n = 2
df.LogRatio.shift(-n)[df.Sample == "CD0695"]

#3    1.91
#Name: LogRatio, dtype: float64

Upvotes: 1

EdChum
EdChum

Reputation: 394329

Use get_loc to get the ordinal position of a specific row passing the index label, then you can use iloc to get the nth row after this row:

In [261]:
indexCD0695 = df.index.get_loc(df[df['Sample']=="CD0695"].index[0])
indexCD0695

Out[261]:
1

In [262]:
n=2
logratio_value = df.iloc[indexCD0695+n]['LogRatio']
logratio_value

Out[262]:
1.9099999999999999

Upvotes: 4

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