This seems to be extremely simple, but if I've got a mental block.
I have a string which contains, say, only '_' and 'x', and I need to find backwards positions of all x-sequences:
xxx___xxx___xxx
___x__xxx_xxx__
What is the fastest approach? Should I use KMP or BM or it's an overkill?
You can scan the string letter by letter. Here's the pseudocode in python:
prev = ''
# enumerate(collection) enumerates collection elements along with their indices
# in the form of tuple (index, element)
# in python strings are collections of characters
for i, c in enumerate(string):
if c == 'x' and c != prev:
print "found x sequence at position %d" % i # (this prints out the index)
prev = c
Related
The program must accept a string S as the input. The program must replace every vowel in the string S by the next consonant (alphabetical order) and replace every consonant in the string S by the next vowel (alphabetical order). Finally, the program must print the modified string as the output.
s=input()
z=[let for let in s]
alpa="abcdefghijklmnopqrstuvwxyz"
a=[let for let in alpa]
v="aeiou"
vow=[let for let in v]
for let in z:
if(let=="a"or let=="e" or let=="i" or let=="o" or let=="u"):
index=a.index(let)+1
if index!="a"or index!="e"or index!="i"or index!="o"or index!="u":
print(a[index],end="")
else:
for let in alpa:
ind=alpa.index(let)
i=ind+1
if(i=="a"or i=="e" or i=="i"or i=="o"or i=="u"):
print(i,end="")
the output is :
i/p orange
pbf
the required output is:
i/p orange
puboif
I would do it like this:
import string
def dumb_encrypt(text, vowels='aeiou'):
result = ''
for char in text:
i = string.ascii_letters.index(char)
if char.lower() in vowels:
result += string.ascii_letters[(i + 1) % len(string.ascii_letters)]
else:
c = 'a'
for c in vowels:
if string.ascii_letters.index(c) > i:
break
result += c
return result
print(dumb_encrypt('orange'))
# puboif
Basically, I would use string.ascii_letters, instead of defining that anew. Also, I would not convert all to list as it is not necessary for looping through. The consonants you got right. The vowels, I would just do an uncertain search for the next valid consonant. If the search, fails it sticks back to default a value.
Here I use groupby to split the alphabet into runs of vowels and consonants. I then create a mapping of letters to the next letter of the other type (ignoring the final consonants in the alphabet). I then use str.maketrans to build a translation table I can pass to str.translate to convert the string.
from itertools import groupby
from string import ascii_lowercase as letters
vowels = "aeiou"
is_vowel = vowels.__contains__
partitions = [list(g) for k, g in groupby(letters, is_vowel)]
mapping = {}
for curr_letters, next_letters in zip(partitions, partitions[1:]):
for letter in curr_letters:
mapping[letter] = next_letters[0]
table = str.maketrans(mapping)
"orange".translate(table)
# 'puboif'
I found this question to be interesting and I would like to share this here and find reasonably good codes, specific to py :
Given a string S having characters from English alphabets ['a' - 'z'] and '.' as the special character (without quotes).
Write a program to construct the lexicographically smallest palindrome by filling each of the faded character ('.') with a lower case alphabet.
Definition:
The smallest lexicographical order is an order relation where string s is smaller than t, given the first character of s (s1 ) is smaller than the first character of t (t1 ), or in case they
are equivalent, the second character, etc.
For example : "aaabbb" is smaller than "aaac" because although the first three characters
are equal, the fourth character b is smaller than the fourth character c.
Input Format:
String S
Output Format:
Print lexicographically smallest palindrome after filling each '.' character, if it
possible to construct one. Print -1 otherwise.
Example-1
Input:
a.ba
Output:
abba
Example-2:
Input:
a.b
Output:
-1
Explanation:
In example 1, you can create a palindrome by filling the '.' character by 'b'.
In example 2, it is not possible to make the string s a palindrome.
You can't just copy paste questions from NPTEL assignments and ask them here without even trying!
Anyways,since the "code" is your only concern,try copy pasting the lines below:
word = input()
length = len(word)
def SmallestPalindrome(word, length):
i = 0
j = length - 1
word = list(word) #creating a list from the input word
while (i <= j):
if (word[i] == word[j] == '.'):
word[i] = word[j] = 'a'
elif word[i] != word[j]:
if (word[i] == '.'):
word[i] = word[j]
elif (word[j] == '.'):
word[j] = word[i]
else: # worst case situation when palindrome condition is not met
return -1
i = i + 1
j = j - 1
return "".join(word) # to turn the list back to a string
print(SmallestPalindrome(word, length)) #Print the output of your function
s=input()
s=list(s)
n=len(s)
j=n
c=0
for i in range(n):
j=j-1
if((s[i]==s[j]) and (i==j) and (s[i]=='.' and s[j]=='.')):
s[i]='a'
s[j]='a'
elif(s[i]==s[j]):
continue
elif((s[i]!=s[j]) and (i!=j) and (s[i]=='.' or s[j]=='.')):
if(s[i]!='.'):
s[j]=s[i]
else:
s[i]=s[j]
elif((i==j) and (s[i]=='.')):
s[i]=a
else:
c=c+1
break
if(c<1):
for k in s:
print(k,end="")
else:print("-1")
I want to convert a string so that the pair positions will be in upper case characters and the impair positions will be in lower case characters.
Here is what I've tried so far:
def foldingo(chaine):
chaineuh=chaine[0::2].upper()
chaine=chaineuh[1::2].lower()
return chaine
your code takes every other character in chaine, uppercases them, and assigns those characters to chaineuh.
Then it takes every other character in chaineuh, lowercases them, and assigns those characters to chaine again. In other words:
abcdefg -> ACEG -> cg
You'll notice it's not keeping the characters that you're not trying to target.
You could try building all the uppercases and lowercases separately, then iterate with zip to get them together.
def fold(s):
uppers = s[0::2].upper()
lowers = s[1::2].lower()
return zip(uppers, lowers)
But this doesn't quit work either, since zip gives you tuples, not strings, and will drop the last character in odd-lengthed strings
abcdefg -> ACEG, bdf -> ('A', 'b'), ('C', 'd'), ('E', 'f')
We could fix that by using a couple calls to str.join and using itertools.zip_longest with a fillvalue='', but it's kind of like using a wrench to hammer in a nail. It's not really the right tool for the job. For the record: it would look like:
''.join([''.join(pair) for pair in itertools.zip_longest(uppers, lowers, fillvalue='')])
yuck.
Let's instead just iterate over the string and uppercase every other letter. We can use an alternating boolean to track whether we're upper'ing or lower'ing this time around.
def fold(s):
time_to_upper = True
result = ""
for ch in s:
if time_to_upper:
result += ch.upper()
else:
result += ch.lower()
time_to_upper = not time_to_upper
return result
You could also use enumerate and a modulo to keep track:
def fold(s):
result = ""
for i, ch in enumerate(s):
ch = ch.lower() if i % 2 else ch.upper()
result += ch
return result
Or by using itertools.cycle, str.join, and list comprehensions, we can make this a lot shorter (possibly at the cost of readability!)
import itertools
def fold(s):
return ''.join([op(ch) for op, ch in zip(itertools.cycle([str.upper, str.lower]), s)]
That's the source code:
def revers_e(str_one,str_two):
for i in range(len(str_one)):
for j in range(len(str_two)):
if str_one[i] == str_two[j]:
str_one = (str_one - str_one[i]).split()
print(str_one)
else:
print('There is no relation')
if __name__ == '__main__':
str_one = input('Put your First String: ').split()
str_two = input('Put your Second String: ')
print(revers_e(str_one, str_two))
How can I remove a letter that occurs in both strings from the first string then print it?
How about a simple pythonic way of doing it
def revers_e(s1, s2):
print(*[i for i in s1 if i in s2]) # Print all characters to be deleted from s1
s1 = ''.join([i for i in s1 if i not in s2]) # Delete them from s1
This answer says, "Python strings are immutable (i.e. they can't be modified). There are a lot of reasons for this. Use lists until you have no choice, only then turn them into strings."
First of all you don't need to use a pretty suboptimal way using range and len to iterate over a string since strings are iterable you can just iterate over them with a simple loop.
And for finding intersection within 2 string you can use set.intersection which returns all the common characters in both string and then use str.translate to remove your common characters
intersect=set(str_one).intersection(str_two)
trans_table = dict.fromkeys(map(ord, intersect), None)
str_one.translate(trans_table)
def revers_e(str_one,str_two):
for i in range(len(str_one)):
for j in range(len(str_two)):
try:
if str_one[i] == str_two[j]:
first_part=str_one[0:i]
second_part=str_one[i+1:]
str_one =first_part+second_part
print(str_one)
else:
print('There is no relation')
except IndexError:
return
str_one = input('Put your First String: ')
str_two = input('Put your Second String: ')
revers_e(str_one, str_two)
I've modified your code, taking out a few bits and adding a few more.
str_one = input('Put your First String: ').split()
I removed the .split(), because all this would do is create a list of length 1, so in your loop, you'd be comparing the entire string of the first string to one letter of the second string.
str_one = (str_one - str_one[i]).split()
You can't remove a character from a string like this in Python, so I split the string into parts (you could also convert them into lists like I did in my other code which I deleted) whereby all the characters up to the last character before the matching character are included, followed by all the characters after the matching character, which are then appended into one string.
I used exception statements, because the first loop will use the original length, but this is subject to change, so could result in errors.
Lastly, I just called the function instead of printing it too, because all that does is return a None type.
These work in Python 2.7+ and Python 3
Given:
>>> s1='abcdefg'
>>> s2='efghijk'
You can use a set:
>>> set(s1).intersection(s2)
{'f', 'e', 'g'}
Then use that set in maketrans to make a translation table to None to delete those characters:
>>> s1.translate(str.maketrans({e:None for e in set(s1).intersection(s2)}))
'abcd'
Or use list comprehension:
>>> ''.join([e for e in s1 if e in s2])
'efg'
And a regex to produce a new string without the common characters:
>>> re.sub(''.join([e for e in s1 if e in s2]), '', s1)
'abcd'
I have a list of words in Pandas (DF)
Words
Shirt
Blouse
Sweater
What I'm trying to do is swap out certain letters in those words with letters from my dictionary one letter at a time.
so for example:
mydict = {"e":"q,w",
"a":"z"}
would create a new list that first replaces all the "e" in a list one at a time, and then iterates through again replacing all the "a" one at a time:
Words
Shirt
Blouse
Sweater
Blousq
Blousw
Swqater
Swwater
Sweatqr
Sweatwr
Swezter
I've been looking around at solutions here: Mass string replace in python?
and have tried the following code but it changes all instances "e" instead of doing so one at a time -- any help?:
mydict = {"e":"q,w"}
s = DF
for k, v in mydict.items():
for j in v:
s['Words'] = s["Words"].str.replace(k, j)
DF["Words"] = s
this doesn't seem to work either:
s = DF.replace({"Words": {"e": "q","w"}})
This answer is very similar to Brian's answer, but a little bit sanitized and the output has no duplicates:
words = ["Words", "Shirt", "Blouse", "Sweater"]
md = {"e": "q,w", "a": "z"}
md = {k: v.split(',') for k, v in md.items()}
newwords = []
for word in words:
newwords.append(word)
for c in md:
occ = word.count(c)
pos = 0
for _ in range(occ):
pos = word.find(c, pos)
for r in md[c]:
tmp = word[:pos] + r + word[pos+1:]
newwords.append(tmp)
pos += 1
Content of newwords:
['Words', 'Shirt', 'Blouse', 'Blousq', 'Blousw', 'Sweater', 'Swqater', 'Swwater', 'Sweatqr', 'Sweatwr', 'Swezter']
Prettyprint:
Words
Shirt
Blouse
Blousq
Blousw
Sweater
Swqater
Swwater
Sweatqr
Sweatwr
Swezter
Any errors are a result of the current time. ;)
Update (explanation)
tl;dr
The main idea is to find the occurences of the character in the word one after another. For each occurence we are then replacing it with the replacing-char (again one after another). The replaced word get's added to the output-list.
I will try to explain everything step by step:
words = ["Words", "Shirt", "Blouse", "Sweater"]
md = {"e": "q,w", "a": "z"}
Well. Your basic input. :)
md = {k: v.split(',') for k, v in md.items()}
A simpler way to deal with replacing-dictionary. md now looks like {"e": ["q", "w"], "a": ["z"]}. Now we don't have to handle "q,w" and "z" differently but the step for replacing is just the same and ignores the fact, that "a" only got one replace-char.
newwords = []
The new list to store the output in.
for word in words:
newwords.append(word)
We have to do those actions for each word (I assume, the reason is clear). We also append the world directly to our just created output-list (newwords).
for c in md:
c as short for character. So for each character we want to replace (all keys of md), we do the following stuff.
occ = word.count(c)
occ for occurrences (yeah. count would fit as well :P). word.count(c) returns the number of occurences of the character/string c in word. So "Sweater".count("o") => 0 and "Sweater".count("e") => 2.
We use this here to know, how often we have to take a look at word to get all those occurences of c.
pos = 0
Our startposition to look for c in word. Comes into use in the next loop.
for _ in range(occ):
For each occurence. As a continual number has no value for us here, we "discard" it by naming it _. At this point where c is in word. Yet.
pos = word.find(c, pos)
Oh. Look. We found c. :) word.find(c, pos) returns the index of the first occurence of c in word, starting at pos. At the beginning, this means from the start of the string => the first occurence of c. But with this call we already update pos. This plus the last line (pos += 1) moves our search-window for the next round to start just behind the previous occurence of c.
for r in md[c]:
Now you see, why we updated mc previously: we can easily iterate over it now (a md[c].split(',') on the old md would do the job as well). So we are doing the replacement now for each of the replacement-characters.
tmp = word[:pos] + r + word[pos+1:]
The actual replacement. We store it in tmp (for debug-reasons). word[:pos] gives us word up to the (current) occurence of c (exclusive c). r is the replacement. word[pos+1:] adds the remaining word (again without c).
newwords.append(tmp)
Our so created new word tmp now goes into our output-list (newwords).
pos += 1
The already mentioned adjustment of pos to "jump over c".
Additional question from OP: Is there an easy way to dictate how many letters in the string I want to replace [(meaning e.g. multiple at a time)]?
Surely. But I have currently only a vague idea on how to achieve this. I am going to look at it, when I got my sleep. ;)
words = ["Words", "Shirt", "Blouse", "Sweater", "multipleeee"]
md = {"e": "q,w", "a": "z"}
md = {k: v.split(',') for k, v in md.items()}
num = 2 # this is the number of replaces at a time.
newwords = []
for word in words:
newwords.append(word)
for char in md:
for r in md[char]:
pos = multiples = 0
current_word = word
while current_word.find(char, pos) != -1:
pos = current_word.find(char, pos)
current_word = current_word[:pos] + r + current_word[pos+1:]
pos += 1
multiples += 1
if multiples == num:
newwords.append(current_word)
multiples = 0
current_word = word
Content of newwords:
['Words', 'Shirt', 'Blouse', 'Sweater', 'Swqatqr', 'Swwatwr', 'multipleeee', 'multiplqqee', 'multipleeqq', 'multiplwwee', 'multipleeww']
Prettyprint:
Words
Shirt
Blouse
Sweater
Swqatqr
Swwatwr
multipleeee
multiplqqee
multipleeqq
multiplwwee
multipleeww
I added multipleeee to demonstrate, how the replacement works: For num = 2 it means the first two occurences are replaced, after them, the next two. So there is no intersection of the replaced parts. If you would want to have something like ['multiplqqee', 'multipleqqe', 'multipleeqq'], you would have to store the position of the "first" occurence of char. You can then restore pos to that position in the if multiples == num:-block.
If you got further questions, feel free to ask. :)
Because you need to replace letters one at a time, this doesn't sound like a good problem to solve with pandas, since pandas is about doing everything at once (vectorized operations). I would dump out your DataFrame into a plain old list and use list operations:
words = DF.to_dict()["Words"].values()
for find, replace in reversed(sorted(mydict.items())):
for word in words:
occurences = word.count(find)
if not occurences:
print word
continue
start_index = 0
for i in range(occurences):
for replace_char in replace.split(","):
modified_word = list(word)
index = modified_word.index(find, start_index)
modified_word[index] = replace_char
modified_word = "".join(modified_word)
print modified_word
start_index = index + 1
Which gives:
Words
Shirt
Blousq
Blousw
Swqater
Swwater
Sweatqr
Sweatwr
Words
Shirt
Blouse
Swezter
Instead of printing the words, you can append them to a list and re-create a DataFrame if that's what you want to end up with.
If you are looping, you need to update s at each cycle of the loop. You also need to loop over v.
mydict = {"e":"q,w"}
s=deduped
for k, v in mydict.items():
for j in v:
s = s.replace(k, j)
Then reassign it to your dataframe:
df["Words"] = s
If you can write this as a function that takes in a 1d array (list, numpy array etc...), you can use df.apply to apply it to any column, using df.apply().