Python – Extract String elements from Mixed Matrix

Given a Matrix, Extract all the elements that are of string data type.

Input : test_list = [[5, 6, 3], ["Gfg", 3], [9, "best", 4]] 
Output : ['Gfg', 'best'] 
Explanation : All strings are extracted.

Input : test_list = [["Gfg", 3], [9, "best", 4]] 
Output : ['Gfg', 'best'] 
Explanation : All strings are extracted. 

Method #1 : Using list comprehension + isinstance()

The combination of above functions can be used to solve this problem. In this, we iterate nested lists using list comprehension and check for string instance using isinstance().

Python3

# Python3 code to demonstrate working of
# Extract String elements from Mixed Matrix
# Using list comprehension + isinstance()

# initializing lists
test_list = [[5, 6, 3], ["Gfg", 3, "is"], [9, "best", 4]]

# printing original list
print("The original list : " + str(test_list))

# strings are extracted using isinstance()
res = [ele for sub in test_list for ele in sub if isinstance(ele, str)]

# printing result
print("The String instances : " + str(res))

Output

The original list : [[5, 6, 3], ['Gfg', 3, 'is'], [9, 'best', 4]]
The String instances : ['Gfg', 'is', 'best']

Time Complexity: O(n) where n is the number of elements in the list “test_list”. 
Auxiliary Space: O(1) additional space is not needed.

Method #2 :  Using chain.from_iterables() + list comprehension + isinstance()

This is yet another way in which this task can be performed. Whole Matrix is flattened and then isinstance() is applied over it to check for string elements in flattened list.

Python3

# Python3 code to demonstrate working of
# Extract String elements from Mixed Matrix
# Using chain.from_iterables + list comprehension + isinstance()
from itertools import chain

# initializing lists
test_list = [[5, 6, 3], ["Gfg", 3, "is"], [9, "best", 4]]

# printing original list
print("The original list : " + str(test_list))

# strings are extracted using isinstance()
# using chain.from_iterables()
res = [ele for ele in chain.from_iterable(test_list) if isinstance(ele, str)]

# printing result
print("The String instances : " + str(res))

Output

The original list : [[5, 6, 3], ['Gfg', 3, 'is'], [9, 'best', 4]]
The String instances : ['Gfg', 'is', 'best']

Method #3 : Using extend() and type() methods

Python3

# Python3 code to demonstrate working of
# Extract String elements from Mixed Matrix

# initializing lists
test_list = [[5, 6, 3], ["Gfg", 3, "is"], [9, "best", 4]]

# printing original list
print("The original list : " + str(test_list))

x=[]
res=[]
for i in test_list:
    x.extend(i)
for i in x:
    if(type(i) is str):
        res.append(i)

# printing result
print("The String instances : " + str(res))

Output

The original list : [[5, 6, 3], ['Gfg', 3, 'is'], [9, 'best', 4]]
The String instances : ['Gfg', 'is', 'best']