Analyze Text Data with String Arrays
This example shows how to store text from a file as a string array, sort the words by their frequency, plot the result, and collect basic statistics for the words found in the file.
Import Text File to String Array
Read text from Shakespeare's Sonnets with the
fileread returns the text as a 1-by-100266 character vector.
sonnets = fileread('sonnets.txt'); sonnets(1:35)
ans = 'THE SONNETS by William Shakespeare'
Convert the text to a string using the
string function. Then, split it on newline characters using the
sonnets becomes a 2625-by-1 string array, where each string contains one line from the poems. Display the first five lines of
sonnets = string(sonnets); sonnets = splitlines(sonnets); sonnets(1:5)
ans = 5x1 string "THE SONNETS" "" "by William Shakespeare" "" ""
Clean String Array
To calculate the frequency of the words in
sonnets, first clean it by removing empty strings and punctuation marks. Then reshape it into a string array that contains individual words as elements.
Remove the strings with zero characters (
"") from the string array. Compare each element of
"", the empty string. You can create strings, including an empty string, using double quotes.
TF is a logical vector that contains a true value wherever
sonnets contains a string with zero characters. Index into
TF and delete all strings with zero characters.
TF = (sonnets == ""); sonnets(TF) = ; sonnets(1:10)
ans = 10x1 string "THE SONNETS" "by William Shakespeare" " I" " From fairest creatures we desire increase," " That thereby beauty's rose might never die," " But as the riper should by time decease," " His tender heir might bear his memory:" " But thou, contracted to thine own bright eyes," " Feed'st thy light's flame with self-substantial fuel," " Making a famine where abundance lies,"
Replace some punctuation marks with space characters. For example, replace periods, commas, and semi-colons. Keep apostrophes because they can be part of some words in the Sonnets, such as light's.
p = [".","?","!",",",";",":"]; sonnets = replace(sonnets,p," "); sonnets(1:10)
ans = 10x1 string "THE SONNETS" "by William Shakespeare" " I" " From fairest creatures we desire increase " " That thereby beauty's rose might never die " " But as the riper should by time decease " " His tender heir might bear his memory " " But thou contracted to thine own bright eyes " " Feed'st thy light's flame with self-substantial fuel " " Making a famine where abundance lies "
Strip leading and trailing space characters from each element of
sonnets = strip(sonnets); sonnets(1:10)
ans = 10x1 string "THE SONNETS" "by William Shakespeare" "I" "From fairest creatures we desire increase" "That thereby beauty's rose might never die" "But as the riper should by time decease" "His tender heir might bear his memory" "But thou contracted to thine own bright eyes" "Feed'st thy light's flame with self-substantial fuel" "Making a famine where abundance lies"
sonnets into a string array whose elements are individual words. You can use the
split function to split elements of a string array on whitespace characters, or on delimiters that you specify. However,
split requires that every element of a string array must be divisible into an equal number of new strings. The elements of
sonnets have different numbers of spaces, and therefore are not divisible into equal numbers of strings. To use the
split function on
sonnets, write a for-loop that calls
split on one element at a time.
Create the empty string array
sonnetWords using the
strings function. Write a for-loop that splits each element of
sonnets using the
split function. Concatenate the output from
sonnetWords. Each element of
sonnetWords is an individual word from
sonnetWords = strings(0); for i = 1:length(sonnets) sonnetWords = [sonnetWords ; split(sonnets(i))]; end sonnetWords(1:10)
ans = 10x1 string "THE" "SONNETS" "by" "William" "Shakespeare" "I" "From" "fairest" "creatures" "we"
Sort Words Based on Frequency
Find the unique words in
sonnetWords. Count them and sort them based on their frequency.
To count words that differ only by case as the same word, convert
sonnetWords to lowercase. For example,
the count as the same word. Find the unique words using the
unique function. Then, count the number of times each unique word occurs using the
sonnetWords = lower(sonnetWords); [words,~,idx] = unique(sonnetWords); numOccurrences = histcounts(idx,numel(words));
Sort the words in
sonnetWords by number of occurrences, from most to least common.
[rankOfOccurrences,rankIndex] = sort(numOccurrences,'descend'); wordsByFrequency = words(rankIndex);
Plot Word Frequency
Plot the occurrences of words in the Sonnets from the most to least common words. Zipf's Law states that the distribution of occurrences of words in a large body text follows a power-law distribution.
loglog(rankOfOccurrences); xlabel('Rank of word (most to least common)'); ylabel('Number of Occurrences');
Display the ten most common words in the Sonnets.
ans = 10x1 string "and" "the" "to" "my" "of" "i" "in" "that" "thy" "thou"
Collect Basic Statistics in Table
Calculate the total number of occurrences of each word in
sonnetWords. Calculate the number of occurrences as a percentage of the total number of words, and calculate the cumulative percentage from most to least common. Write the words and the basic statistics for them to a table.
numOccurrences = numOccurrences(rankIndex); numOccurrences = numOccurrences'; numWords = length(sonnetWords); T = table; T.Words = wordsByFrequency; T.NumOccurrences = numOccurrences; T.PercentOfText = numOccurrences / numWords * 100.0; T.CumulativePercentOfText = cumsum(numOccurrences) / numWords * 100.0;
Display the statistics for the ten most common words.
ans=10×4 table Words NumOccurrences PercentOfText CumulativePercentOfText ______ ______________ _____________ _______________________ "and" 490 2.7666 2.7666 "the" 436 2.4617 5.2284 "to" 409 2.3093 7.5377 "my" 371 2.0947 9.6324 "of" 370 2.0891 11.722 "i" 341 1.9254 13.647 "in" 321 1.8124 15.459 "that" 320 1.8068 17.266 "thy" 280 1.5809 18.847 "thou" 233 1.3156 20.163
The most common word in the Sonnets, and, occurs 490 times. Together, the ten most common words account for 20.163% of the text.