Thomas Matthew Thomas Matthew - 24 days ago 11
Python Question

Export pandas dataframe as an interaction file: row \t value \t col

With the below pd dataframe:

print(df)
A B C
X 1 2 3
Y 4 5 6
Z 7 8 9


I need to create a simple interaction network file, or SIF file, of the format:

node1 xx node2
node1 xx node2
node1 yy node2
.
.
.


Where each line is an interaction on a df: row label, value, column label. Below is an iterative (and naive) approach to writing such a file:

with open ('interaction.sif', 'w') as sif:
for row in df.index:
for col in df.columns:
sif.write('{}\t{}\t{}'.format(row, df[col][row], col))


The inefficient code above offers the ideal sif file for the dataframe
df
:

X 1 A
X 2 B
X 3 C
Y 4 A
Y 5 B
Y 6 C
Z 7 A
Z 8 B
Z 9 C


Is there a dataframe method to write to a csv or table, for example, in the format above? Or is there a way to vectorize this operation?

Answer

You need stack with reset_index:

df = df.stack().reset_index()
df.columns = list('ABC')
df = df[['A','C','B']]
print (df)
   A  C  B
0  X  1  A
1  X  2  B
2  X  3  C
3  Y  4  A
4  Y  5  B
5  Y  6  C
6  Z  7  A
7  Z  8  B
8  Z  9  C

And then DataFrame.to_csv:

print (df.to_csv(sep='\t', index=None, header=None))
X       1       A
X       2       B
X       3       C
Y       4       A
Y       5       B
Y       6       C
Z       7       A
Z       8       B
Z       9       C

df.to_csv('interaction.sif', sep='\t', index=None, header=None)
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