Reading text files (readtable, textscan) in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of readtable with mixed data types

What is the output of the following MATLAB code snippet when reading a text file with mixed numeric and text columns?

MATLAB

fid = fopen('data.txt','w');
fprintf(fid, 'ID Age Name\n1 25 Alice\n2 30 Bob\n3 22 Carol');
fclose(fid);
T = readtable('data.txt');
disp(T);

A A table with variables: ID (double), Age (double), Name (string) and 3 rows showing the data

B A table with variables: ID (double), Age (double), Name (cell) and 3 rows showing the data

C Error: File not found

D A numeric matrix with values [1 25; 2 30; 3 22]

💡 Hint

readtable automatically detects variable types and reads text columns as strings or categorical by default.

readtable reads the file and creates a table with columns matching the data types. Numeric columns become double, text columns become string arrays.

❓ Predict Output

intermediate

Output of textscan with delimiter and format specifiers

What is the output of this MATLAB code reading a text file with textscan?

MATLAB

fid = fopen('data2.txt','w');
fprintf(fid, 'John,25,180.5\nJane,30,165.2\n');
fclose(fid);
fid = fopen('data2.txt','r');
C = textscan(fid, '%s %d %f', 'Delimiter', ',');
fclose(fid);
disp(C);

A A 1x3 cell array: {1x2 cell of strings, [25 30], [180.5 165.2]}

B A 1x3 cell array: {1x2 cell of strings, [25;30], [180.5;165.2]}

C A numeric matrix with values [25 180.5; 30 165.2]

D Error: Format specifier mismatch

💡 Hint

textscan returns a cell array with each cell containing a column of data matching the format specifiers.

The format '%s %d %f' reads a string, an integer, and a float per line. The delimiter ',' splits the fields. textscan returns a cell array with each column as a separate cell.

🔧 Debug

advanced

Identify the error in textscan usage

What error does this MATLAB code produce when trying to read a file with textscan?

MATLAB

fid = fopen('data3.txt','w');
fprintf(fid, 'A 10\nB 20\n');
fclose(fid);
fid = fopen('data3.txt','r');
C = textscan(fid, '%s %d %f');
fclose(fid);

A Error: Not enough input arguments for format specifiers

B Error: File not found

C No error, returns a cell array with 3 columns

D Error: Invalid format specifier

💡 Hint

Check if the number of format specifiers matches the number of data columns in the file.

The file has two columns per line, but the format string expects three columns (%s %d %f). This mismatch causes an error.

❓ Predict Output

advanced

Result of readtable with missing data and options

What is the output of this MATLAB code reading a file with missing values using readtable?

MATLAB

fid = fopen('data4.txt','w');
fprintf(fid, 'Name,Score,Age\nAlice,90,25\nBob,,30\nCarol,85,\n');
fclose(fid);
opts = detectImportOptions('data4.txt');
opts = setvaropts(opts, 'Score', 'TreatAsMissing', '');
opts = setvaropts(opts, 'Age', 'TreatAsMissing', '');
T = readtable('data4.txt', opts);
disp(T);

A Table with zeros in place of missing numeric data

B Table with empty strings in Score and Age columns for missing data

C Error: Missing data not handled

D Table with missing numeric values as NaN in Score and Age columns for Bob and Carol

💡 Hint

readtable with import options can treat empty fields as missing and convert them to NaN for numeric columns.

Setting 'TreatAsMissing' to empty string tells readtable to treat empty fields as missing values. Numeric missing values become NaN in the table.

🧠 Conceptual

expert

Choosing between readtable and textscan for large files

Which statement best explains when to prefer textscan over readtable for reading large text files in MATLAB?

A textscan cannot handle mixed data types, so readtable is better for any file with text and numbers

B readtable is always faster and better for large files because it automatically detects formats

C textscan is preferred when you need fine control over reading format and want to process data line-by-line efficiently

D readtable requires manual format specification, while textscan automatically detects data types

💡 Hint

Consider flexibility and performance when reading large files with complex formats.

textscan allows detailed control of format and can read data incrementally, which is useful for large files. readtable is convenient but may be slower and less flexible.