Sixth lecture
Contents
Strings
s1='This is a string'
s1 =
'This is a string'
s2='this IS a string'
s2 =
'this IS a string'
s3='Also a string'
s3 =
'Also a string'
Strings are vectors, (you can ask the size of them, or index them). As vectors, you can't compare them if they have different length.
They are in the ASCII-table, you can ask they number, by converting them to double:
double(s1)
ans =
Columns 1 through 13
84 104 105 115 32 105 115 32 97 32 115 116 114
Columns 14 through 16
105 110 103
There are several builtin functions for handling string. For example this converts to lowercase.
lower(s1)
ans =
'this is a string'
This comperes to strings, giving back a logical scalar.
strcmp(s1,s2)
ans = logical 0
This comparison doesn't mind the lower case- upper-case differences:
strcmpi(s1,s2)
ans = logical 1
You cant concatenate them:
[s1 s2]
ans =
'This is a stringthis IS a string'
Convert string meaning numbers to their actual value as numbers.
s5='12'
a5=str2num(s5)
whos
s5 =
'12'
a5 =
12
Name Size Bytes Class Attributes
a5 1x1 8 double
ans 1x32 64 char
data1 13x15 1560 double
everything 13x16 24882 cell
i 1x1 2 char
numberofletter 1x26 208 double
numbers 13x15 1560 double
p 1x1 8 double
position 1x1 8 double
s1 1x16 32 char
s2 1x16 32 char
s3 1x13 26 char
s5 1x2 4 char
st 1x527 1054 char
stl 1x527 1054 char
texts 13x16 23562 cell
v 1x1 8 double
value 1x1 8 double
Cell matrices
With the help of cell matrices we can store different type of data in one matrix. We create it by telling its size:
data1=cell(2,3)
data1 =
2×3 cell array
{0×0 double} {0×0 double} {0×0 double}
{0×0 double} {0×0 double} {0×0 double}
You have to use curly brackets for indexing:
data1{1,1}='Here'
data1 =
2×3 cell array
{'Here' } {0×0 double} {0×0 double}
{0×0 double} {0×0 double} {0×0 double}
data1{1,2}=12
data1 =
2×3 cell array
{'Here' } {[ 12]} {0×0 double}
{0×0 double} {0×0 double} {0×0 double}
data1{1,3}=[2 4 1]
data1 =
2×3 cell array
{'Here' } {[ 12]} {1×3 double}
{0×0 double} {0×0 double} {0×0 double}
This is not the elemenet of the cell matrix
data1(1,3)
ans =
1×1 cell array
{1×3 double}
Importing data from excel:
We can easily import data from excel files using the xlsread function. For example:
data1=xlsread('adatok.xls')
data1 =
Columns 1 through 7
1.0000 2.0000 3.0000 4.0000 0.3000 5.0000 6.0000
10.0000 10.0000 NaN 10.0000 NaN NaN 9.5000
10.0000 10.0000 NaN NaN NaN 0 9.0000
10.0000 10.0000 10.0000 10.0000 NaN 8.0000 NaN
10.0000 10.0000 5.0000 10.0000 NaN 10.0000 2.0000
10.0000 9.0000 10.0000 10.0000 NaN 8.0000 5.0000
10.0000 10.0000 10.0000 4.0000 NaN 4.0000 2.0000
10.0000 NaN 10.0000 10.0000 NaN 5.0000 8.0000
10.0000 7.0000 NaN NaN NaN 5.0000 NaN
10.0000 8.0000 6.0000 10.0000 NaN 10.0000 10.0000
10.0000 10.0000 NaN 10.0000 NaN NaN 9.5000
10.0000 10.0000 5.0000 10.0000 NaN 10.0000 8.0000
10.0000 9.0000 4.5000 7.0000 NaN 8.0000 9.0000
Columns 8 through 14
7.0000 8.0000 0.3000 9.0000 10.0000 11.0000 12.0000
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
NaN NaN NaN NaN NaN NaN NaN
Column 15
NaN
39.5000
29.0000
48.0000
47.0000
52.0000
40.0000
43.0000
22.0000
54.0000
39.5000
53.0000
47.5000
[numbers, texts, everything]=xlsread('adatok.xls');
Polimorphic functions
Built-in functions can be called different ways. For example:
rand
ans =
0.1712
gives one random (?) number
rand(4)
ans =
0.7060 0.0971 0.9502 0.7655
0.0318 0.8235 0.0344 0.7952
0.2769 0.6948 0.4387 0.1869
0.0462 0.3171 0.3816 0.4898
gives a 4*4 matrix
rand(3,4)
ans =
0.4456 0.7547 0.6551 0.4984
0.6463 0.2760 0.1626 0.9597
0.7094 0.6797 0.1190 0.3404
gives a 3*4 matrix.
This is a polymorphic function, that is it works even if it's called with different number of inputs, and the output depends on the number of inputs. We can write such functions with the help of the nargin function. The output of the nargin function is the number of input our function was called.
Let us make a multiplication table. If our function was called without an input, then the output should be a 10*10 table, if there was one input, then a squared table, if two inputs was given, say n an m, then a n*m sized table.
function out1=multiP(n,m) if nargin==0 n=10; m=10; elseif nargin==1 m=n; end v1=1:n; v2=1:m; out1=v1'*v2;
Similarly to nargin, nargout gives us the number of outputs when the function was called.
min([1, 5 -1])
ans =
-1
[p, v]=min([1, 5, -1])
p =
-1
v =
3
Recommended problems
1. problem: Consider the following text: A neuron or, also known as a neurone, is an electrically excitable cell that receives, processes, and transmits information through electrical and chemical signals. These signals between neurons occur via specialized connections called synapses. Neurons can connect to each other to form neural networks. Neurons are the primary components of the central nervous system, which includes the brain and spinal cord, and of the peripheral nervous system, which comprises the autonomic nervous system and the somatic nervous system.
Create a variable called st, which contains this text as a string. Find out
- how many characters are in the text
- how many letter are there (look for a suitable function in the documentation)
- what is the most frequent letter?
2. problem Make a function called ceasarS(s), which takes a string as an input. The output is a string, where every letter is shifted by one in the abc, expect for z, which is changed to a. Also write the decoding function.
3. problem: Write a function called findOut(s), which takes a string (which is the name of an excel file) as input. The outputs are the number of numbers in the excel file, and the minimum and maximum of them.
4. problem Write a function called swapP(v,a,b), which takes a v vector, and two doubles as input. The output is a modified v: every element in v, which equals to a should be exchanged by b. If the function was called swapP(v,a), then every element equals to a should be exchanged to 1, if it was called swapP(v), then every 0 should be changed to 1.