What I am trying to accomplish: Pull the last 8 characters from the lines in a file, slice them into two character chunks, compare those chunks with my dictionary, and list the results. This is literally the first thing I have done in python, and my head is spinning with all the answers here.
I think I need basic swimming instruction, and every answer seems to be a primer on free-diving for world records.
I am using the following code (Right now I have the h1 through h4 commented out because it is not returning keys that are in my dictionary):
d1 = {'30': 0, '31': 1, '32': 2, '33' : 3, '34': 4, '35': 5, '36': 6, '37': 7, '38': 8, '39': 9,
'41': 'A', '42': 'B', '43': 'C', '44': 'D', '45': 'E', '46': 'F'}
filename = raw_input("Filename? > ")
with open(filename) as file:
for line in iter(file.readline, ''):
h1 = line[-8:-6]
h2 = line[-6:-4]
h3 = line[-4:-2]
h4 = line[-2:]
#h1 = d1[h1]
#h2 = d1[h2]
#h3 = d1[h3]
#h4 = d1[h4]
print h1,h2,h3,h4
Here is part of the txt file I am using as input:
naa.60000970000192600748533031453442
naa.60000970000192600748533031453342
naa.60000970000192600748533031453242
naa.60000970000192600748533031453142
naa.60000970000192600748533031434442
naa.60000970000192600748533031434342
naa.60000970000192600748533031434242
naa.60000970000192600748533032363342
When I run my script, here is the output generated by the code above:
14 53 44 2
14 53 34 2
14 53 24 2
14 53 14 2
14 34 44 2
14 34 34 2
14 34 24 2
32 36 33 42
The last line looks exactly as I would expect. All the other lines have been shifted or have dropped characters. I am at a loss for this...I have tried many different ways to open the file in python, but have been unable to get them to loop through, or had other issues.
Is there a simple fix I am just missing here? Thanks, j
I suspect that what's going on is that each line you read has a carriage return at the end, except the last one. So the last one is right, but the others are basically splitting the last part of the string. IOW, I think your file lines look something like
>>> open("demo.txt").readline()
'naa.60000970000192600748533031453442\n'
where the \n is the symbol for the carriage return, and is only one character (it's not \ + n). I might write your code something like
with open(filename) as myfile:
for line in myfile:
line = line.strip() # get rid of leading and trailing whitespace
h1 = line[-8:-6]
h2 = line[-6:-4]
h3 = line[-4:-2]
h4 = line[-2:]
print h1,h2,h3,h4
which for me produces
Filename? > demo.txt
31 45 34 42
31 45 33 42
31 45 32 42
31 45 31 42
31 43 44 42
31 43 43 42
31 43 42 42
32 36 33 42
We could simplify the h parts, but we'll leave that alone for now. :^)
Related
So, i'm doing a beginners challenge on HackerHank and, a strange behavior of ruby is boggling my mind.
The challenge is: find and count how many pairs there are in the array. (sock pairs)
Here's my code.
n = 100
ar = %w(50 49 38 49 78 36 25 96 10 67 78 58 98 8 53 1 4 7 29 6 59 93 74 3 67 47 12 85 84 40 81 85 89 70 33 66 6 9 13 67 75 42 24 73 49 28 25 5 86 53 10 44 45 35 47 11 81 10 47 16 49 79 52 89 100 36 6 57 96 18 23 71 11 99 95 12 78 19 16 64 23 77 7 19 11 5 81 43 14 27 11 63 57 62 3 56 50 9 13 45)
def sockMerchant(n, ar)
counter = 0
ar.each do |item|
if ar.count(item) >= 2
counter += ar.count(item)/2
ar.delete(item)
end
end
counter
end
print sockMerchant(n, ar)
The problem is, it doesn't count well. after running the function, in it's internal array ar still have countable pairs, and i prove it by running it again.
There's more. If you sort the array, it behaves differently.
it doesnt make sense to me.
you can check the behavior on this link
https://repl.it/repls/HuskyFrighteningNaturallanguage
You're deleting items from a collection while iterating over it - expect bad stuff to happen. In short, don't do that if you don't want to have such problems, see:
> arr = [1,2,1]
# => [1, 2, 1]
> arr.each {|x| puts x; arr.delete(x) }
# 1
# => [2]
We never get the 2 in our iteration.
A simple solution, that is a small variation of your code, could look as follows:
def sock_merchant(ar)
ar.uniq.sum do |item|
ar.count(item) / 2
end
end
Which is basically finding all unique socks, and then counting pairs for each of them.
Note that its complexity is n^2 as for each unique element n of the array, you have to go through the whole array in order to find all elements that are equal to n.
An alternative, first group all socks, then check how many pairs of each type we have:
ar.group_by(&:itself).sum { |k,v| v.size / 2 }
As ar.group_by(&:itself), short for ar.group_by { |x| x.itself } will loop through the array and create a hash looking like this:
{"50"=>["50", "50"], "49"=>["49", "49", "49", "49"], "38"=>["38"], ...}
And by calling sum on it, we'll iterate over it, summing the number of found elements (/2).
I have a 3x3x2000 array of rotation matrices that I need to transform into a 2000x9 array.
I think I have to use a combination of permute() and reshape(), but I don't get the correct output order.
This is what I need:
First row of 3x3 array needs to be columns 1:3 in the output
Second row of 3x3 array needs to be columns 4:6 in the output
Third row of 3x3 array needs to be columns 7:9 in the output
I have tried all possible combinations of numbers 1 2 3 in the following code:
out1 = permute(input, [2 3 1]);
out2 = reshape(out1, [2000 9]);
But I always end up with the wrong order. Any tips for a Matlab newbie?
How about a simple for-loop?
for i=1:size(myinput,3)
myoutput(i,:)=[myinput(1,:,i) myinput(2,:,i) myinput(3,:,i)];
% or
% myoutput(i,:)=reshape(myinput(:,:,i),[],9);
end
It's not simple as using permute and reshape, but it is transparent and easier for debugging. Once everything in your program runs perfectly, you can consider to rewrite such for-loops in your code...
You had a mix-up in your permute
a = reshape(1:9*6, 3, 3, []);
a is a 3x3x6 matrix, each
a(:,:,i) = 9*(i-1) + [1 4 7
2 5 8
3 6 9];
So
out1 = permute(a, [3,1,2]);
out2 = reshape(out1, [], 9);
Or in one line
out3 = reshape(permute(a, [3,1,2]), [], 9);
So
out2 = out3 =
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54
I have an array in MATLAB
For example
a = 1:100;
I want to select the first 4 element in every successive 10 elements.
In this example I want to b will be
b = [1,2,3,4,11,12,13,14, ...]
can I do it without for loop?
I read in the internet that i can select the element for each step:
b = a(1:10:end);
but this is not working for me.
Can you help me?
With reshape
%// reshaping your matrix to nx10 so that it has successive 10 elements in each row
temp = reshape(a,10,[]).'; %//'
%// taking first 4 columns and reshaping them back to a row vector
b = reshape(temp(:,1:4).',1,[]); %//'
Sample Run for smaller size (although this works for your actual dimensions)
a = 1:20;
>> b
b =
1 2 3 4 11 12 13 14
To vectorize the operation you must generate the indices you wish to extract:
a = 1:100;
b = a(reshape(bsxfun(#plus,(1:4)',0:10:length(a)-1),[],1));
Let's break down how this works. First, the bsxfun function. This performs a function, here it is addition (#plus) on each element of a vector. Since you want elements 1:4 we make this one dimension and the other dimension increases by tens. this will lead a Nx4 matrix where N is the number of groups of 4 we wish to extract.
The reshape function simply vectorizes this matrix so that we can use it to index the vector a. To better understand this line, try taking a look at the output of each function.
Sample Output:
>> b = a(reshape(bsxfun(#plus,(1:4)',0:10:length(a)-1),[],1))
b =
Columns 1 through 19
1 2 3 4 11 12 13 14 21 22 23 24 31 32 33 34 41 42 43
Columns 20 through 38
44 51 52 53 54 61 62 63 64 71 72 73 74 81 82 83 84 91 92
Columns 39 through 40
93 94
I need to loop through coloumn 1 of a matrix and return (i) when I have come across ALL of the elements of another vector which i can predefine.
check_vector = [1:43] %% I dont actually need to predefine this - i know I am looking for the numbers 1 to 43.
matrix_a coloumn 1 (which is the only coloumn i am interested in looks like this for example
1
4
3
5
6
7
8
9
10
11
12
13
14
16
15
18
17
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
1
3
4
2
6
7
8
We want to loop through matrix_a and return the value of (i) when we have hit all of the numbers in the range 1 to 43.
In the above example we are looking for all the numbers from 1 to 43 and the iteration will end round about position 47 in matrix_a because it is at this point that we hit number '2' which is the last number to complete all numbers in the sequence 1 to 43.
It doesnt matter if we hit several of one number on the way, we count all those - we just want to know when we have reached all the numbers from the check vector or in this example in the sequence 1 to 43.
Ive tried something like:
completed = []
for i = 1:43
complete(i) = find(matrix_a(:,1) == i,1,'first')
end
but not working.
Assuming A as the input column vector, two approaches could be suggested here.
Approach #1
With arrayfun -
check_vector = [1:43]
idx = find(arrayfun(#(n) all(ismember(check_vector,A(1:n))),1:numel(A)),1)+1
gives -
idx =
47
Approach #2
With customary bsxfun -
check_vector = [1:43]
idx = find(all(cumsum(bsxfun(#eq,A(:),check_vector),1)~=0,2),1)+1
To find the first entry at which all unique values of matrix_a have already appeared (that is, if check_vector consists of all unique values of matrix_a): the unique function almost gives the answer:
[~, ind] = unique(matrix_a, 'first');
result = max(ind);
Someone might have a more compact answer but is this what your after?
maxIndex = 0;
for ii=1:length(a)
[f,index] = ismember(ii,a);
maxIndex=max(maxIndex,max(index));
end
maxIndex
Here is one solution without a loop and without any conditions on the vectors to be compared. Given two vectors a and b, this code will find the smallest index idx where a(1:idx) contains all elements of b. idx will be 0 when b is not contained in a.
a = [ 1 4 3 5 6 7 8 9 10 11 12 13 14 16 15 18 17 19 20 21 22 23 24 25 26 ...
27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 1 3 4 2 6 7 8 50];
b = 1:43;
[~, Loca] = ismember(b,a);
idx = max(Loca) * all(Loca);
Some details:
ismember(b,a) checks if all elements of b can be found in a and the output Loca lists the indices of these elements within a. The index will be 0, if the element cannot be found in a.
idx = max(Loca) then is the highest index in this list of indices, so the smallest one where all elements of b are found within a(1:idx).
all(Loca) finally checks if all indices in Loca are nonzero, i.e. if all elements of b have been found in a.
Is there any character or character combination that MATLAB interprets as comments, when importing data from text files? Being that when it detects it at the beginning of a line, will know all the line is to ignore?
I have a set of points in a file that look like this:
And as you can see he doesn't seem to understand them very well. Is there anything other than // I could use that MATLAB knows it's to ignore?
Thanks!
Actually, your data is not consistent, as you must have the same number of column for each line.
1)
Apart from that, using '%' as comments will be correctly recognized by importdata:
file.dat
%12 31
12 32
32 22
%abc
13 33
31 33
%ldddd
77 7
66 6
%33 33
12 31
31 23
matlab
data = importdata('file.dat')
2)
Otherwise use textscan to specify arbitrary comment symbols:
file2.dat
//12 31
12 32
32 22
//abc
13 33
31 33
//ldddd
77 7
66 6
//33 33
12 31
31 23
matlab
fid = fopen('file2.dat');
data = textscan(fid, '%f %f', 'CommentStyle','//', 'CollectOutput',true);
data = cell2mat(data);
fclose(fid);
If you use the function textscan, you can set the CommentStyle parameter to // or %. Try something like this:
fid = fopen('myfile.txt');
iRow = 1;
while (~feof(fid))
myData(iRow,:) = textscan(fid,'%f %f\n','CommentStyle','//');
iRow = iRow + 1;
end
fclose(fid);
That will work if there are two numbers per line. I notice in your examples the number of numbers per line varies. There are some lines with only one number. Is this representative of your data? You'll have to handle this differently if there isn't a uniform number of columns in each row.
Have you tried %, the default comment character in MATLAB?
As Amro pointed out, if you use importdata this will work.