arr = [3, 4, 5]
extended_arr = [1, 2, *arr]
#df = df[['gene_symbol', 'sample_id', 'fc']]
df = df.pivot(index='gene_symbol',columns='sample_id',values='fc')
print (df)
sample_id S1 S2
gene_symbol
a 100.0 1.3
b 100.0 14.0
c 112.0 125.0