for i=1:N
f(i) = 'f'+i;
end
gives an error in MatLab. What's the correct syntax to initialize an array with N strings of the pattern fi?
It seems like even this is not working:
for i=1:4
f(i) = 'f';
end
You can concatenate strings using strcat. If you plan on concatenating numbers as strings, you must first use num2str to convert the numbers to strings.
Also, strings can't be stored in a vector or matrix, so f must be defined as a cell array, and must be indexed using { and } (instead of normal round brackets).
f = cell(N, 1);
for i=1:N
f{i} = strcat('f', num2str(i));
end
For versions prior to R2014a...
One easy non-loop approach would be to use genvarname to create a cell array of strings:
>> N = 5;
>> f = genvarname(repmat({'f'}, 1, N), 'f')
f =
'f1' 'f2' 'f3' 'f4' 'f5'
For newer versions...
The function genvarname has been deprecated, so matlab.lang.makeUniqueStrings can be used instead in the following way to get the same output:
>> N = 5;
>> f = strrep(matlab.lang.makeUniqueStrings(repmat({'f'}, 1, N), 'f'), '_', '')
f =
1×5 cell array
'f1' 'f2' 'f3' 'f4' 'f5'
Let me add another solution:
>> N = 5;
>> f = cellstr(num2str((1:N)', 'f%d'))
f =
'f1'
'f2'
'f3'
'f4'
'f5'
If N is more than two digits long (>= 10), you will start getting extra spaces. Add a call to strtrim(f) to get rid of them.
As a bonus, there is an undocumented built-in function sprintfc which nicely returns a cell arrays of strings:
>> N = 10;
>> f = sprintfc('f%d', 1:N)
f =
'f1' 'f2' 'f3' 'f4' 'f5' 'f6' 'f7' 'f8' 'f9' 'f10'
Using sprintf was already proposed by ldueck in a comment, but I think this is worth being an answer:
f(i) = sprintf('f%d', i);
This is in my opinion the most readable solution and also gives some nice flexibility (i.e. when you want to round a float value, use something like %.2f).
according to this it looks like you have to set "N" before trying to use it and it looks like it needs to be an int not string? Don't know much bout MatLab but just what i gathered from that site..hope it helps :)
Try the following:
for i = 1:4
result = strcat('f',int2str(i));
end
If you use this for naming several files that your code generates, you are able to concatenate more parts to the name. For example, with the extension at the end and address at the beginning:
filename = strcat('c:\...\name',int2str(i),'.png');
Related
The task is:
User enters a number, you take 1 number from the left, one from the right and sum it. Then you take the rest of this number and sum every digit in it. then you get two answers. You have to sort them from biggest to lowest and make them into a one solid number. I solved it, but i don't like how it looks like. i mean the task is pretty simple but my code looks like trash. Maybe i should use some more built-in functions and libraries. If so, could you please advise me some? Thank you
a = int(input())
b = [int(i) for i in str(a)]
closesum = 0
d = []
e = ""
farsum = b[0] + b[-1]
print(farsum)
b.pop(0)
b.pop(-1)
print(b)
for i in b:
closesum += i
print(closesum)
d.append(int(closesum))
d.append(int(farsum))
print(d)
for i in sorted(d, reverse = True):
e += str(i)
print(int(e))
input()
You can use reduce
from functools import reduce
a = [0,1,2,3,4,5,6,7,8,9]
print(reduce(lambda x, y: x + y, a))
# 45
and you can just pass in a shortened list instead of poping elements: b[1:-1]
The first two lines:
str_input = input() # input will always read strings
num_list = [int(i) for i in str_input]
the for loop at the end is useless and there is no need to sort only 2 elements. You can just use a simple if..else condition to print what you want.
You don't need a loop to sum a slice of a list. You can also use join to concatenate a list of strings without looping. This implementation converts to string before sorting (the result would be the same). You could convert to string after sorting using map(str,...)
farsum = b[0] + b[-1]
closesum = sum(b[1:-2])
"".join(sorted((str(farsum),str(closesum)),reverse=True))
I have the following code in Matlab:
a = zeros(23,1)
b = zeros(23,1)
c = zeros(23,1)
How can I write it more compactly? I was looking for a solution that is something like this:
str = {'a','b','c'}
for i = str{i}
i = zeros(23,1)
end
But I can't find a way to do it properly without an error message. Can someone help please?
Here is a compact way using deal :
[a, b, c] = deal(zeros(23,1));
You can also use a struct if the variable name is important:
str = {'a','b','c'};
data = struct
for ii = 1:numel(str)
data.(str{ii}) = zeros(23,1);
end
The struct is more efficient than the table. You can now address data.a, data.b, etc.
But if the name is not useful, it's best to put your data into a cell array:
N = 3;
data = cell(N,1);
for ii = 1:N
data{ii} = zeros(23,1);
end
or simply:
data = cell(3,1);
[data{:}] = deal(zeros(23,1));
Now you address your arrays as data{1}, data{2}, etc., and they're always easy to address in loops.
What you're tempted to do is very bad practise, but can be done like this
str = {'a','b','c'};
for ii = 1:numel(str)
eval( [str{ii} ' = zeros(23,1)'] );
end
Why is this bad practise?
Your code legibility has just gone way down, you can't clearly see where variables are declared.
eval should be avoided
You could use deal to make things a bit nicer, but this doesn't use the array of variable names
[a, b, c] = deal( zeros(23, 1) );
Even better, it's likely you can optimise your code by using a matrix or table instead of separate 1D arrays. The table option means you can still use your variable name array, but you're not using eval for anything!
% Matrix
M = zeros( 23, 3 ); % Index each column as a/b/c using M(:,1) etc
% Table, index using T.a, T.b, T.c
T = array2table( zeros(23,3), 'VariableNames', {'a','b','c'} );
Given two lists (a and b), I'd like to replace three elements of list 'a' with three elements of list 'b'. Currently I am using an expression like this:
a[0], a[5], a[7] = b[11], b[99], b[2]
As I need to do such operations very frequently with lots of different arrays I am wondering if there is a more compact solution for this problem (the number of elements I need to replace is always 3 though). I was thinking about something like:
a[0,5,7] = b[11,99,2]
Which obviously does not work.
If you've a python list you can do something like this :
toReplace = [0,5,7]
targetIndices = [11, 99, 2]
for i,j in zip(toReplace, targetIndices): a[i] = b[j]
If you've a numpy array, it's even simpler :
a[toReplace] = b[targetIndices]
#i.e, a[[0,5,7]] = b[[11, 99, 2]]
There might be some better solutions but this does the trick:
ind1 = [0,5,7]
ind2 = [11,99,2]
for i in range(len(ind1)):
a[ind1[i]]=b[ind2[i]]
I have another question that I'd like input on, of course no direct answers just something to point me in the right direction!
I have a string of numbers ex. 1234567890 and I want 1 & 0 to change places (0 and 9) and for '2345' & '6789' to change places. For a final result of '0678923451'.
First things I did was convert the string into a list with:
ex. original = '1234567890'
original = list(original)
original = ['0', '1', '2' etc....]
Now, I get you need to pull the first and last out, so I assigned
x = original[0]
and
y = original[9]
So: x, y = y, x (which gets me the result I'm looking for)
But how do I input that back into the original list?
Thanks!
The fact that you 'pulled' the data from the list in variables x and y doesn't help at all, since those variables have no connection anymore with the items from the list. But why don't you swap them directly:
original[0], original[9] = original[9], original[0]
You can use the slicing operator in a similar manner to swap the inner parts of the list.
But, there is no need to create a list from the original string. Instead, you can use the slicing operator to achieve the result you want. Note that you cannot swap the string elements as you did with lists, since in Python strings are immutable. However, you can do the following:
>>> a = "1234567890"
>>> a[9] + a[5:9] + a[1:5] + a[0]
'0678923451'
>>>
I have two cell arrays of string A and B. All cells of B are also in A. I want to find the index of cell of B in A. Thanks.
Example:
A=
'aaaa'
'bbbb'
'cccc'
'dddd'
'ffff'
B=
'ffff'
'aaaa'
ans=
5
1
or
ans=
1
5
use either intersect or ismember
[~, idxInA] = intersect(A,B)
or
LocInA = find(ismember(A,B))
You can do this really simply, use the code below
indices = cell(size(B));
for i = 1:numel(B)
indices{i} = find(strcmpi(A,B(i)));
end
While I do recommend using ismember or intersect, those solutions will not handle case insensitive solutions. Also, those methods will not indicate how many times a specific index was matched, where my solution, will return all indices that match for each comparison.
UPDATE
Code I am running to test this.
A={'aaaa','bbbb','cccc','dddd','ffff','aaaa'};
B={'ffff','aaaa','cccc','qwerty'};
indices = cell(size(B));
for i = 1:numel(B)
indices{i} = find(strcmpi(A,B(i)));
end
indices
Which returns the following
indices =
[5] [1x2 double] [3] [1x0 double]
I do not see where you are having problems