Transposing Every nth row to column in a large dataset
Hey is Python or other tools an option here? Since you mentioned it is a large dataset, you might want to iterate over it instead of loading all of them at once. 

Here is a solution in Python:

import pandas as pd
from collections import defaultdict


inputs = [
'cat1/: Topic1_Variable1',
'cat2/: Topic1_Variable2',
'cat3/: Topic1_Variable3',
'cat4/: Topic1_Variable4',
'cat1/: Topic2_Variable1',
'cat2/: Topic2_Variable2',
'cat3/: Topic2_Variable3',
'cat4/: Topic2_Variable4',
'cat1/: Topic3_Variable1',
'cat2/: Topic3_Variable2',
'cat3/: Topic3_Variable3',
'cat4/: Topic3_Variable4',]


outputs = defaultdict(list)

for item in inputs:
    cat, topic = item.split('/: ')
    outputs[cat].append(topic)

print pd.DataFrame(outputs)


Output:

               cat1              cat2              cat3              cat4
0  Topic1_Variable1  Topic1_Variable2  Topic1_Variable3  Topic1_Variable4
1  Topic2_Variable1  Topic2_Variable2  Topic2_Variable3  Topic2_Variable4
2  Topic3_Variable1  Topic3_Variable2  Topic3_Variable3  Topic3_Variable4