Reading text files (readtable, textscan) in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read a table from 'data.csv' using readtable.

MATLAB

T = [1]('data.csv');

Drag options to blanks, or click blank then click option'

Areadtable

Btextscan

Cfopen

Dload

Attempts:

3 left

💡 Hint

Common Mistakes

Using fopen instead of readtable

Using load which is for MAT-files

The readtable function reads data from a file into a table.

2fill in blank

medium

Complete the code to open a text file named 'file.txt' for reading.

MATLAB

fid = [1]('file.txt', 'r');

Drag options to blanks, or click blank then click option'

Areadtable

Bfopen

Ctextscan

Dfclose

Attempts:

3 left

💡 Hint

Common Mistakes

Using readtable which reads tables, not opening files

Using fclose which closes files

fopen opens a file and returns a file identifier for reading or writing.

3fill in blank

hard

Fix the error in the code to read numeric data from a file using textscan.

MATLAB

fid = fopen('numbers.txt', 'r');
data = [1](fid, '%f');
fclose(fid);

Drag options to blanks, or click blank then click option'

Atextscan

Bfopen

Creadtable

Dfclose

Attempts:

3 left

💡 Hint

Common Mistakes

Using fopen instead of textscan to read data

Using readtable which reads tables, not formatted data

textscan reads formatted data from an open file identified by fid.

4fill in blank

hard

Fill both blanks to read a CSV file with headers and convert it to a table.

MATLAB

opts = detectImportOptions('data.csv');
opts.[1] = 1;
T = [2]('data.csv', opts);

Drag options to blanks, or click blank then click option'

AVariableNamesLine

Breadtable

CDelimiter

Dtextscan

Attempts:

3 left

💡 Hint

Common Mistakes

Using textscan instead of readtable for tables

Setting Delimiter instead of VariableNamesLine

Setting VariableNamesLine to 1 tells MATLAB to use the first line as headers. Then readtable reads the file using these options.

5fill in blank

hard

Fill all three blanks to read a file line by line using textscan and close it.

MATLAB

fid = [1]('log.txt', 'r');
data = [2](fid, '%s', 'Delimiter', '\n');
[3](fid);

Drag options to blanks, or click blank then click option'

Afopen

Btextscan

Cfclose

Dreadtable

Attempts:

3 left

💡 Hint

Common Mistakes

Using readtable instead of fopen or fclose

Not closing the file after reading

First, open the file with fopen. Then read lines as strings with textscan. Finally, close the file with fclose.

Practice

1. What is the main advantage of using readtable in MATLAB to read text files?

easy

A. It reads files without opening them first.

B. It requires manual specification of each data type.

C. It only reads numeric data, ignoring text.

D. It automatically loads data into a table with proper formatting.

Solution

1. Step 1: Understand readtable functionality

   readtable is designed to load text files directly into tables, automatically detecting and formatting columns.

2. Step 2: Compare options

   It automatically loads data into a table with proper formatting. correctly describes this automatic loading and formatting. Other options describe incorrect behaviors.

3. Final Answer:

   It automatically loads data into a table with proper formatting. -> Option D

4. Quick Check:

   readtable = automatic table loading [OK]

Hint: Remember: readtable = easy table import [OK]

Common Mistakes:

• Thinking readtable needs manual type input
• Assuming readtable only reads numbers
• Believing files don't need opening before reading

2. Which of the following is the correct syntax to open a text file named data.txt for reading in MATLAB?

easy

A. fileID = fopen('data.txt', 'r');

B. fileID = open('data.txt', 'r');

C. fileID = readfile('data.txt');

D. fileID = textscan('data.txt', 'r');

Solution

1. Step 1: Recall file opening function

   In MATLAB, fopen is used to open files with a mode like 'r' for reading.

2. Step 2: Check each option

   fileID = fopen('data.txt', 'r'); uses fopen correctly. fileID = open('data.txt', 'r'); uses a non-existent open function. fileID = readfile('data.txt'); uses readfile which is not a MATLAB function. fileID = textscan('data.txt', 'r'); misuses textscan which reads from an open file, not opens it.

3. Final Answer:

   fileID = fopen('data.txt', 'r'); -> Option A

4. Quick Check:

   Open file = fopen(filename, 'r') [OK]

Hint: Use fopen to open files before reading [OK]

Common Mistakes:

• Using open instead of fopen
• Trying to read file directly without fopen
• Confusing textscan with fopen

3. Given the following MATLAB code snippet, what will be the output stored in data?

fileID = fopen('numbers.txt', 'r');
data = textscan(fileID, '%d %f');
fclose(fileID);

Assuming numbers.txt contains:

10 3.14
20 2.71
30 1.62

medium

A. A 1x2 cell array with first cell [10;20;30] and second cell [3.14;2.71;1.62]

B. A 3x2 numeric matrix with all numbers

C. A single numeric array combining all values

D. An error because textscan cannot read mixed data

Solution

1. Step 1: Understand textscan output format

   textscan returns a cell array where each cell contains a column of data matching the format specifiers.

2. Step 2: Analyze the format and file content

   Format '%d %f' reads an integer and a float per line. The file has 3 lines, so the first cell will be [10;20;30] and the second cell [3.14;2.71;1.62].

3. Final Answer:

   A 1x2 cell array with first cell [10;20;30] and second cell [3.14;2.71;1.62] -> Option A

4. Quick Check:

   textscan returns cell array columns [OK]

Hint: textscan returns cells, each for one format column [OK]

Common Mistakes:

• Expecting a numeric matrix instead of cell array
• Thinking textscan merges all data into one array
• Assuming textscan cannot read mixed types

4. Consider this MATLAB code snippet:

fileID = fopen('data.txt', 'r');
data = textscan(fileID, '%s %d');

What is the main problem with this code?

medium

A. textscan cannot read strings and integers together.

B. The format specifier '%s %d' is invalid.

C. The file is not closed after reading.

D. fopen should be called with 'w' mode to read.

Solution

1. Step 1: Check file handling steps

   The code opens the file with fopen and reads with textscan, but does not close the file.

2. Step 2: Validate format and usage

   The format '%s %d' is valid for reading a string and an integer. textscan supports mixed types. fopen with 'r' is correct for reading.

3. Final Answer:

   The file is not closed after reading. -> Option C

4. Quick Check:

   Always fclose after fopen [OK]

Hint: Always fclose after reading files [OK]

Common Mistakes:

• Forgetting to close the file
• Thinking '%s %d' is invalid format
• Confusing fopen modes

5. You have a text file records.txt with mixed data: a name (string), age (integer), and height (float) on each line, separated by commas, like:

John,25,5.9
Anna,30,5.5
Mike,22,6.1

Which MATLAB approach correctly reads this file into a table with proper data types?

hard

A. Use readtable('records.txt', 'Delimiter', ',', 'Format', '%s%d%f')

B. Use readtable('records.txt') without specifying delimiter

C. Use textscan(fopen('records.txt', 'r'), '%s %d %f', 'Delimiter', ',') and fclose after

D. Use textscan(fopen('records.txt'), '%s %d %f') without closing file

Solution

1. Step 1: Identify correct reading method for mixed CSV data into table

   readtable automatically detects common delimiters like commas and loads data into a table with inferred types (string for names, double for numbers).

2. Step 2: Compare options

   Use readtable('records.txt') without specifying delimiter: readtable('records.txt') auto-detects comma delimiter. Use readtable('records.txt', 'Delimiter', ',', 'Format', '%s%d%f') uses invalid 'Format' parameter (readtable lacks it). Use textscan(fopen('records.txt', 'r'), '%s %d %f', 'Delimiter', ',') and fclose after: textscan syntax invalid ('Delimiter' not for fid), returns cell array not table. Use textscan(fopen('records.txt'), '%s %d %f') without closing file: textscan fails to parse commas (default whitespace), no fclose.

3. Final Answer:

   Use readtable('records.txt') without specifying delimiter -> Option B

4. Quick Check:

   readtable = auto delimiter + table types [OK]

Hint: readtable auto-detects CSV delimiters into tables [OK]

Common Mistakes:

• Using textscan expecting table output
• Adding invalid 'Format' to readtable
• Omitting delimiter handling in textscan