lambda 表达式和过滤器 function 从列表中提取单词

Question

I am writing a program that extracts all list elements starting from 'b' using lambda expression and filter function, but I am just getting empty []'.

In []:

x = ['bread','rice','butter','beans','pizza','lasagna','eggs']

criteria = lambda value:value==['b']  
     
c_list = list(filter(criteria,x))
c_list

Out[]:

 []

Answer 1

You can use filter and lambda together

list(filter(lambda item: item.startswith('b'), x))

EXPLANATION :

lambda function will either return True or False based on whether string item startwsith b and filter will just call the same lambda function for each item in the list, and will keep only the records for which lambda returns True value, Finally, you need to type cast it to a list, since filter function gives a filter object which is an iterable .

OUTPUT :

['bread', 'butter', 'beans']

You can just update your lambda expression to check the first character in the value parameter: Either: criteria = lambda value:value[0]==['b'] or: criteria = lambda value:value.startswith('b')

Answer 2

Check the first value of the word using indexing.

x = ['bread','rice','butter','beans','pizza','lasagna','eggs']

criteria = lambda value:value[0]=='b'
     
c_list = list(filter(criteria,x))

print(c_list)

prints

['bread', 'butter', 'beans']

Answer 3

We can try using a list comprehension here as well:

inp = ['bread','rice','butter','beans','pizza','lasagna','eggs']
output = [x for x in inp if x.startswith('b')]
print(output)  # ['bread', 'butter', 'beans']