I am having a problem with an xor search.
I have an array composed of binary values. My list contains 1000 distinct binary values, and I want to time how long it takes for a double loop to find an element in the list. Therefore for a double loop search, I expect it to go through the loop [(1) + (2) +(3)+...+(1000)] = 500500 times. [n(n+1) / 2]
I use the bitwise_xor in the following code
from numpy import bitwise_xor
count = 0
for word1 in listOutTextnoB:
for word2 in listOutTextnoB:
count+=1
if bitwise_xor(word1,word2)==0:
break
print "count"
Unfortunately, when I print count, I get count = 1,000,000
If I change the if statement to
if bitwise_xor(word1,word2):
break
count is 1000
I also tried to do:
if word1^word2==0:
break
but it gives me "TypeError: unsupported operand type(s) for ^: 'str' and 'str'"
A working example would be:
1101110111010111011101101110110010111100101111001 XOR 1101110111010111011101101110110010111100101111001
it should give me 0 and exit the inner loop
What is wrong with code?
^ works on integers, not arrays, so that is not surprising.
I don't know why you used strings but:
from numpy import bitwise_xor
listOutTextnoB = range(1000)
count = 0
for word1 in listOutTextnoB:
for word2 in listOutTextnoB:
count+=1
if bitwise_xor(word1,word2)==0:
break
print "count", count
prints
count 500500
as you predict.
EDIT: yes, you should be doing
if int(word1) ^ int(word2) == 0:
break
bitwise_xor is actually returning 'NotImplemented' for every string, string input.
Your error shows the problem: the values in your list are strings, not numbers. I'm not sure what bitwise_xor does to them, but I'm pretty sure it won't convert them to numbers first. If you do this manually (bitwise_xor (int (word1), int (word2))), I think it should work.
Related
I would like to extract integers from strings from a cell array in Matlab. Each string contains 1 or 2 integers formatted as shown below. Each number can be one or two digits. I would like to convert each string to a 1x2 array. If there is only one number in the string, the second column should be -1. If there are two numbers then the first entry should be the first number, and the second entry should be the second number.
'[1, 2]'
'[3]'
'[10, 3]'
'[1, 12]'
'[11, 12]'
Thank you very much!
I have tried a few different methods that did not work out. I think that I need to use regex and am having difficulty finding the proper expression.
You can use str2num to convert well formatted chars (which you appear to have) to the correct arrays/scalars. Then simply pad from the end+1 element to the 2nd element (note this is nothing in the case there's already two elements) with the value -1.
This is most clearly done in a small loop, see the comments for details:
% Set up the input
c = { ...
'[1, 2]'
'[3]'
'[10, 3]'
'[1, 12]'
'[11, 12]'
};
n = cell(size(c)); % Initialise output
for ii = 1:numel(n) % Loop over chars in 'c'
n{ii} = str2num(c{ii}); % convert char to numeric array
n{ii}(end+1:2) = -1; % Extend (if needed) to 2 elements = -1
end
% (Optional) Convert from a cell to an Nx2 array
n = cell2mat(n);
If you really wanted to use regex, you could replace the loop part with something similar:
n = regexp( c, '\d{1,2}', 'match' ); % Match between one and two digits
for ii = 1:numel(n)
n{ii} = str2double(n{ii}); % Convert cellstr of chars to arrays
n{ii}(end+1:2) = -1; % Pad to be at least 2 elements
end
But there are lots of ways to do this without touching regex, for example you could erase the square brackets, split on a comma, and pad with -1 according to whether or not there's a comma in each row. Wrap it all in a much harder to read (vs a loop) cellfun and ta-dah you get a one-liner:
n = cellfun( #(x) [str2double( strsplit( erase(x,{'[',']'}), ',' ) ), -1*ones(1,1-nnz(x==','))], c, 'uni', 0 );
I'd recommend one of the loops for ease of reading and debugging.
How do I return the first x words from a file which has some content which is greater in length than a particular cut_off value? If file has less words than x then the function should be able to return all words in the file which is greater than cut_off:
My code is:
def function(filename , x , cut_off):
output=""
index=0
myfile=open(filename)
text=myfile.read()
words=text.split()
while(index < x):
if(len(words[index])>cut_off):
output+=words[index]
index+=1
return output
I am still soooo confused!
Please help me out
You could use the following also:
Keep a counter = 0
1. Read the file line by line.
2. Split each line into a list of words.
3. Loop through each of these words and compare with the cut_off.
4. If the word satisfies the cut off, increment the counter.
5. Now check if the counter is less than x or not.
6. If it is less, add the word to a list and keep looping to the next word or line.
7. If equal, return the list of the words.
This takes care of each of your problems.
Let me know in case you need a proper code for this.
I want to limit the size of a list in python 2.7 I have been trying to do it with a while loop but it doesn't work
l=[]
i=raw_input()//this is the size of the list
count=0
while count<i:
l.append(raw_input())
count=count+1
The thing is that it does not finish the loop. I think this problem has an easy answer but I can't find it.
Thanks in advance
I think the problem is here:
i=raw_input()//this is the size of the list
raw_input() returns a string, not an integer, so comparisons between i and count don't make sense. [In Python 3, you'd get the error message TypeError: unorderable types: int() < str(), which would have made things clear.] If you convert i to an int, though:
i = int(raw_input())
it should do what you expect. (We'll ignore error handling etc. and possibly converting what you're adding to l if you need to.)
Note though that it would be more Pythonic to write something like
for term_i in range(num_terms):
s = raw_input()
l.append(s)
Most of the time you shouldn't need to manually keep track of indices by "+1", so if you find yourself doing it there's probably a better way.
That is because i has a string value type, and int < "string" always returns true.
What you want is:
l=[]
i=raw_input() #this is the size of the list
count=0
while count<int(i): #Cast to int
l.append(raw_input())
count=count+1
You should try changing your code to this:
l = []
i = input() //this is the size of the list
count = 0
while count < i:
l.append(raw_input())
count+=1
raw_input() returns a string while input() returns an integer. Also count+=1 is better programming practice than count = count + 1. Good luck
based on this function. I'm trying to create two empty arrays (one for x and other for y), which later I will use to plot in python. But before anything this is what I have so far...
import math
x1=-2.0
x2=2.0
arr1 = []
arr2 = []
i=0
n=10
delta=(x2-x1)/n
for i in range (0,n+1):
x=x1+delta*i
arr1.append(x)
print arr1
# I have not called the w function yet
the code above creates a list of 10 numbers for now to keep it simple. Then it will send the elements of the array to the function below and compute the equation with certain numbers(infinite loop).
#This function will create the array list for y
import math
def w(x, limit):# the limit here to compare when the number is really small
suma = 0.0
sumb = 0.0
m=1
x=0
suma=suma+((1/(math.pow(2,m))*(math.sin(math.pow(2,m)*x)))
sumb=suma+((1/(math.pow(2,m+1))*(math.sin(math.pow(2,m+1)*x))) # I'm having a
#syntax error
#here
x+=0
if (abs (suma-sumb)<limit):
break:
else m+=1:
if (m<20):
break:
I will appreciate any help with my syntax errors or any suggestion. I just hope I was clear enough.
Thanks ahead of time
The syntax error is actually on the previous line, where the parenthesis are not balanced. You need an extra ) at the end of that line (and at the one you indicated as giving an error too btw).
There are also a few other issues
suma is set to zero, so suma = suma + ... is the same as suma = ..., but I'm guessing you still need to add while loop before this line.
On the line indicated, you have sumb = suma +, which is probably a copy/paste mistake.
The code block starting at x+=0 is indented by only 3 spaces instead of 4. This is probably not the case in your actual code, but if it is, Python will complain about that too.
else m+=1: should be else: m+=1 (colon directly after else, not at the end of the line.
break: should just be break (without to colon).
In my c++ class, we got assigned pairs. Normally I can come up with an effective algorithm quite easily, this time I cannot figure out how to do this to save my life.
What I am looking for is someone to explain an algorithm (or just give me tips on what would work) in order to get this done. I'm still at the planning stage and want to get this code done on my own in order to learn. I just need a little help to get there.
We have to create histograms based on a 4 or 5 integer input. It is supposed to look something like this:
Calling histo(5, 4, 6, 2) should produce output that appears like:
*
* *
* * *
* * *
* * * *
* * * *
-------
A B C D
The formatting to this is just killing me. What makes it worse is that we cannot use any type of arrays or "advanced" sorting systems using other libraries.
At first I thought I could arrange the values from highest to lowest order. But then I realized I did not know how to do this without using the sort function and I was not sure how to go on from there.
Kudos for anyone who could help me get started on this assignment. :)
Try something along the lines of this:
Determine the largest number in the histogram
Using a loop like this to construct the histogram:
for(int i = largest; i >= 1; i--)
Inside the body of the loop, do steps 3 to 5 inclusive
If i <= value_of_column_a then print a *, otherwise print a space
Repeat step 3 for each column (or write a loop...)
Print a newline character
Print the horizontal line using -
Print the column labels
Maybe i'm mistaken on your q, but if you know how many items are in each column, it should be pretty easy to print them like your example:
Step 1: Find the Max of the numbers, store in variable, assign to column.
Step 2: Print spaces until you get to column with the max. Print star. Print remaining stars / spaces. Add a \n character.
Step 3: Find next max. Print stars in columns where the max is >= the max, otherwise print a space. Add newline. at end.
Step 4: Repeat step 3 (until stop condition below)
when you've printed the # of stars equal to the largest max, you've printed all of them.
Step 5: add the -------- line, and a \n
Step 6: add row headers and a \n
If I understood the problem correctly I think the problem can be solved like this:
a= <array of the numbers entered>
T=<number of numbers entered> = length(a) //This variable is used to
//determine if we have finished
//and it will change its value
Alph={A,B,C,D,E,F,G,..., Z} //A constant array containing the alphabet
//We will use it to print the bottom row
for (i=1 to T) {print Alph[i]+" "}; //Prints the letters (plus space),
//one for each number entered
for (i=1 to T) {print "--"}; //Prints the two dashes per letter above
//the letters, one for each
while (T!=0) do {
for (i=1 to N) do {
if (a[i]>0) {print "*"; a[i]--;} else {print " "; T--;};
};
if (T!=0) {T=N};
}
What this does is, for each non-zero entered number, it will print a * and then decrease the number entered. When one of the numbers becomes zero it stops putting *s for its column. When all numbers have become zero (notice that this will occur when the value of T comes out of the for as zero. This is what the variable T is for) then it stops.
I think the problem wasn't really about histograms. Notice it also doesn't require sorting or even knowing the