Search a list using a string

Question

I have a List of Lists:

 A = [['andy', 'dear', 'boy', 'tobe', 'todo'], 
      ['where', 'what', 'when', 'how'], 
      ['korea', 'japan', 'china', 'usa'], 
      ['tweet', 'where', 'why', 'how']]

I have three questions to be exact:

1. How do I retrieve a sub-list from this list using a particular element as a keyword?
   For instance, I want to retrieve all the lists having element 'why' in them? What is
   the best possible way of doing so?
2. How do I retrieve a sub-list from this list using a part of a particular element as a keyword?
   For instance, I want to retrieve all the lists having elements containing 'wh' as beginning
   characters of any of the elements?
3. How do I get the position or index of resulting sub-lists from any of these two searching methods?

I am familiar with the concept of retrieving all the elements from a list with matching with a particular keyword, but its confusing when it comes to retrieve all the lists matching a particular keyword...

Any guesses? Thanks in advance.

Answer 1

Simple and straight

elem = 'why'
index_li = []
for idx, item in enumerate(A):
    for word in item:
        if word.startswith(elem):
            index_li.append(idx)
            break
print index_li

Example

>>> elem = 'wh'
... index_li = []
... for idx, item in enumerate(A):
...     for word in item:
...         if word.startswith(elem):
...             print word, item
...             index_li.append(idx)
...             break
... print index_li
where ['where', 'what', 'when', 'how']
where ['tweet', 'where', 'why', 'how']
[1, 3]

Answer 2

I love list comprehensions and functional programming, so here's that approach

A

sub_list_a = [ el for el in A if 'why' in el ]

B

sub_list_b = [ el for el in A if any( ['wh' in s for s in el] ) ]

A little more difficult to read, but concise and sensible.

C

Then to get the indices of where each of the sub_lists were found

location_a = [ ii for ii, el in enumerate(A) if el in sub_list_a ]

Simply replace b for a to get the locations for part b.

Answer 3

For first:

>>> for l in A:
...     if 'why' in l:
...             print l
... 
['tweet', 'where', 'why', 'how']

For the second:(wy any where)

>>> for l in A:
...     for i in l:
...             if 'wh' in i:
...                     print l
...                     break
... 
['where', 'what', 'when', 'how']
['tweet', 'where', 'why', 'how']

to test at beginning try this: (using startswith() from @Harido)

>>> for l in A:
...     for i in l:
...             if i.startswith('wh'):
...                     print l
...                     break
... 
['where', 'what', 'when', 'how']
['tweet', 'where', 'why', 'how']

For third:

To find index, you can use A.index(l) method after print stamens for example:

>>> for l in A:
...     for i in l:
...             if 'wh' in i:
...                     print l
...                     print A.index(l)
...                     break
... 
['where', 'what', 'when', 'how']
1
['tweet', 'where', 'why', 'how']
3

But remember I am not good in Python. Some one can give you better ways. (I am writing C like code that is poor) I would like to share this link: Guido van Rossum

Edit:

thanks to @Jaime to suggesting me for k, l in enumerate(A):

>>> for k, l in enumerate(A):
...     for i in l:
...             if 'wh' in i:
...                     print l
...                     print "index =", k
...                     break
... 
['where', 'what', 'when', 'how']
index = 1
['tweet', 'where', 'why', 'how']
index = 3

Answer 4

For all the answers combined:

mylist = [['andy', 'dear', 'boy', 'tobe', 'todo'], ['where', 'what', 'when', 'how'], ['korea', 'japan', 'china', 'usa'], ['tweet', 'where', 'why', 'how']]
for num, sublist in enumerate(mylist):
    if 'why' in sublist:
        print sublist
    for ele in sublist:
        if ele.startswith('wh'):
            print ele, num