Text Data

• character arrays (char data type):

  • a 1 by n character array is also known as a vector array

• string arrays (string data type):

  • a m by n string array is also known as a string

  • a 1 by 1 string array is also known as a string scalar

• cell arrays (cell data type)

what are the different types of text data types

• enclosed by single quotes

  • e.g. message = ‘Hello’

• each character is stored as an element in an array (above example has 5 elements)

• can be created using the input function

  • » name = input (‘Please enter your name:’ ‘,’ ‘s’)

    → Please enter your name: (name)

    name = (name)

how do we use character vectors

• char

• num2str

• int2str

what functions do we use to convert numeric codes into characters

double or +0

what function do we use to convert characters to numeric code values

use round brackets

how do we access elements

use square brackets

how do we concatenate

• newStr = lower(str)

• newStr = upper(str)

  • where str is the character vector we want to convert

  • newStr is the transformed character vector

how do we change the case of our text

• use == with caution

  • generally avoid when working with character vectors

    → generates an error if character vectors aren’t the same length

    → for equal length vectors produces a logical array (not a single logical value)

    → behaves differently when using strings

comparing text data

• tf = strcmp (s1, s2)

  • where s1 is a character vector

  • s2 is a character vector

  • tf is a logical value indicating whether the character vectors are identical (logical 1) or not identical (logical 0)

• tf = strncmp (s1, s2, n)

  • where n is an integer indicating the first n characters to compare

• tf = strncmpi (s1,s2,)

  → ignores capitalisation

how do we use the strcmp function to compare character vectors

• s = sprintf (format, data 1, …, data N)

  • where format is a character vector with format specifiers defining how to write the data

  • data 1, …, data N are the values or variables containing data to write out

  • s is a formatted character vector with each format specifier replaced by the formatted data

how do we format text data

• s → character vector or string array

• c → single character

• d or i → decimal integer

• e → scientific notation

• f → decimal floating point

• g → the shorter of e or f

what are the character conversions

\n

what character do we use to move to a new line

• data = sscanf (s, format, size)

  • s is the text data to scan

  • format is a character vector detailing the data format we wish to read

  • size (optional), read enough data to fill an array with size cfInsizeA

  • data is the data extracted as a column vector

sscanf

• k = strfind (str, pat)

  • str is a character vector to search in

  • pat is a character vector find in str

  • k is a numeric array that contains the starting index of each occurrence of pat in str

strfind

• use double quotes

  • e.g. str_message = “Hello World”

• contain a single string element

• think of it as a container that holds a sequence of characters

• you can extract the character vector from the container using curly braces {}

• will work with the string comparison and formatting functions

string scalars

• size and length

  • a string scalar is a container that holds one character vector

• converting string scalars to numeric codes

  • If the string scalar is a text representation of a number, the double function will convert the string scalar into a numerical value:

    • >> double("100") = 100

  • To obtain the ASCII codes of the text stored in a string scalar, we need to access the character vector or convert it with the char function:

    • >> S = "Hello"; >> double(S{1}) = 72 101 108 108 111

    • >> S = "World"; >> double(char(S)) = 87 111 114 108 100

• accessing elements

  • To access one or more string scalar elements, we first we must first access the character vector (i.e., with brace {} operators) before using standard 1D array indexing with parenthesis () operators.

• concatenation

  • to concatenate string scalars together, we use the addition + operator

  • alternatively, we can use the strcat function with string scalars

  • however, if we use the strcat function with character vectors, it will strip trailing whitespace characters

• comparing string scalars

  • recall that if we use the equality == operator to compare character vectors, MATLAB will throw an error when the character vectors have different lengths

  • this error does not occur when we compare string scalars with the equality == operator

what are the difference between string scalars and character vectors

use the {} operators, e.g. myCellArray = {'hello', "world", [1 6]; 5, "Peter", "Bier"};

how do we create cell arrays