Create and Work with Tables (2024)

This example shows how to create a table from workspace variables, work with table data, and write tables to files for later use.tableis a data type for collecting heterogeneous data and metadata properties such as variable names, row names, descriptions, and variable units, in a single container.

Tables are suitable for column-oriented or tabular data that are often stored as columns in a text file or in a spreadsheet. Each variable in a table can have a different data type, but must have the same number of rows. However, variables in a table are not restricted to column vectors. For example, a table variable can contain a matrix with multiple columns as long as it has the same number of rows as the other table variables. A typical use for a table is to store experimental data, where rows represent different observations and columns represent different measured variables.

Tables are convenient containers for collecting and organizing related data variables and for viewing and summarizing data. For example, you can extract variables to perform calculations and conveniently add the results as new table variables. When you finish your calculations, write the table to a file to save your results.

Create and View Table

Create a table from workspace variables and view it. Alternatively, use theImport Toolor thereadtablefunction to create a table from a spreadsheet or a text file. When you import data from a file using these functions, each column becomes a table variable.

Load sample data for 100 patients from thepatientsMAT-file to workspace variables.

load patientswhos

 Name Size Bytes Class Attributes Age 100x1 800 double Diastolic 100x1 800 double Gender 100x1 11412 cell Height 100x1 800 double LastName 100x1 11616 cell Location 100x1 14208 cell SelfAssessedHealthStatus 100x1 11540 cell Smoker 100x1 100 logical Systolic 100x1 800 double Weight 100x1 800 double

Populate a table with column-oriented variables that contain patient data. You can access and assign table variables by name. When you assign a table variable from a workspace variable, you can assign the table variable a different name.

Create a table and populate it with theGender,Smoker,Height, andWeightworkspace variables. Display the first five rows.

T = table(Gender,Smoker,Height,Weight);T(1:5,:)

ans=5×4 table Gender Smoker Height Weight __________ ______ ______ ______ {'Male' } true 71 176 {'Male' } false 69 163 {'Female'} false 64 131 {'Female'} false 67 133 {'Female'} false 64 119

As an alternative, use thereadtablefunction to read the patient data from a comma-delimited file.readtablereads all the columns that are in a file.

Create a table by reading all columns from the file,patients.dat.

T2 = readtable('patients.dat');T2(1:5,:)

ans=5×10 table LastName Gender Age Location Height Weight Smoker Systolic Diastolic SelfAssessedHealthStatus ____________ __________ ___ _____________________________ ______ ______ ______ ________ _________ ________________________ {'Smith' } {'Male' } 38 {'County General Hospital' } 71 176 1 124 93 {'Excellent'} {'Johnson' } {'Male' } 43 {'VA Hospital' } 69 163 0 109 77 {'Fair' } {'Williams'} {'Female'} 38 {'St. Mary's Medical Center'} 64 131 0 125 83 {'Good' } {'Jones' } {'Female'} 40 {'VA Hospital' } 67 133 0 117 75 {'Fair' } {'Brown' } {'Female'} 49 {'County General Hospital' } 64 119 0 122 80 {'Good' }

You can assign more column-oriented table variables using dot notation,T.varname, whereTis the table andvarnameis the desired variable name. Create identifiers that are random numbers. Then assign them to a table variable, and name the table variableID. All the variables you assign to a table must have the same number of rows. Display the first five rows ofT.

T.ID = randi(1e4,100,1);T(1:5,:)

ans=5×5 table Gender Smoker Height Weight ID __________ ______ ______ ______ ____ {'Male' } true 71 176 8148 {'Male' } false 69 163 9058 {'Female'} false 64 131 1270 {'Female'} false 67 133 9134 {'Female'} false 64 119 6324

All the variables you assign to a table must have the same number of rows.

View the data type, description, units, and other descriptive statistics for each variable by creating a table summary using thesummaryfunction.

summary(T)

Variables: Gender: 100x1 cell array of character vectors Smoker: 100x1 logical Values: True 34 False 66 Height: 100x1 double Values: Min 60 Median 67 Max 72 Weight: 100x1 double Values: Min 111 Median 142.5 Max 202 ID: 100x1 double Values: Min 120 Median 5485.5 Max 9706

Return the size of the table.

size(T)

Access Data by Row and Variable Names

Add row names toTand index into the table using row and variable names instead of numeric indices. Add row names by assigning theLastNameworkspace variable to theRowNamesproperty ofT.

T.Properties.RowNames = LastName;

Display the first five rows ofTwith row names.

T(1:5,:)

ans=5×5 table Gender Smoker Height Weight ID __________ ______ ______ ______ ____ Smith {'Male' } true 71 176 8148 Johnson {'Male' } false 69 163 9058 Williams {'Female'} false 64 131 1270 Jones {'Female'} false 67 133 9134 Brown {'Female'} false 64 119 6324

Return the size ofT. The size does not change because row and variable names are not included when calculating the size of a table.

size(T)

ans = 1×2 100 5

Select all the data for the patients with the last names'Smith'and'Johnson'. In this case, it is simpler to use the row names than to use numeric indices.Tnewis a 2-by-5 table.

Tnew = T({'Smith','Johnson'},:)

Tnew=2×5 table Gender Smoker Height Weight ID ________ ______ ______ ______ ____ Smith {'Male'} true 71 176 8148 Johnson {'Male'} false 69 163 9058

Select the height and weight of the patient named'Johnson'by indexing on variable names.Tnewis a 1-by-2 table.

Tnew = T('Johnson',{'Height','Weight'})

Tnew=1×2 table Height Weight ______ ______ Johnson 69 163

You can access table variables either with dot syntax, as inT.Height, or by named indexing, as inT(:,'Height').

Calculate and Add Result as Table Variable

You can access the contents of table variables, and then perform calculations on them using MATLAB® functions. Calculate body-mass-index (BMI) based on data in the existing table variables and add it as a new variable. Plot the relationship ofBMIto a patient's status as a smoker or a nonsmoker. Add blood-pressure readings to the table, and plot the relationship of blood pressure to BMI.

CalculateBMIusing the table variables,WeightandHeight. You can extractWeightandHeightfor the calculation while conveniently keepingWeight,Height, andBMIin the table with the rest of the patient data. Display the first five rows ofT.

T.BMI = (T.Weight*0.453592)./(T.Height*0.0254).^2;T(1:5,:)

ans=5×6 table Gender Smoker Height Weight ID BMI __________ ______ ______ ______ ____ ______ Smith {'Male' } true 71 176 8148 24.547 Johnson {'Male' } false 69 163 9058 24.071 Williams {'Female'} false 64 131 1270 22.486 Jones {'Female'} false 67 133 9134 20.831 Brown {'Female'} false 64 119 6324 20.426

Populate the variable units and variable descriptions properties forBMI. You can add metadata to any table variable to describe further the data contained in the variable.

T.Properties.VariableUnits{'BMI'} = 'kg/m^2';T.Properties.VariableDescriptions{'BMI'} = 'Body Mass Index';

Create a histogram to explore whether there is a relationship between smoking and body-mass-index in this group of patients. You can index intoBMIwith the logical values from theSmokertable variable, because each row containsBMIandSmokervalues for the same patient.

tf = (T.Smoker == false);h1 = histogram(T.BMI(tf),'BinMethod','integers');hold ontf = (T.Smoker == true);h2 = histogram(T.BMI(tf),'BinMethod','integers');xlabel('BMI (kg/m^2)');ylabel('Number of Patients');legend('Nonsmokers','Smokers');title('BMI Distributions for Smokers and Nonsmokers');hold off

Add blood pressure readings for the patients from the workspace variablesSystolicandDiastolic. Each row containsSystolic,Diastolic, andBMIvalues for the same patient.

T.Systolic = Systolic;T.Diastolic = Diastolic;

Create a histogram to show whether there is a relationship between high values ofDiastolicandBMI.

tf = (T.BMI <= 25);h1 = histogram(T.Diastolic(tf),'BinMethod','integers');hold ontf = (T.BMI > 25);h2 = histogram(T.Diastolic(tf),'BinMethod','integers');xlabel('Diastolic Reading (mm Hg)');ylabel('Number of Patients');legend('BMI <= 25','BMI > 25');title('Diastolic Readings for Low and High BMI');hold off

Reorder Table Variables and Rows for Output

To prepare the table for output, reorder the table rows by name, and table variables by position or name. Display the final arrangement of the table.

Sort the table by row names so that patients are listed in alphabetical order.

T = sortrows(T,'RowNames');T(1:5,:)

ans=5×8 table Gender Smoker Height Weight ID BMI Systolic Diastolic __________ ______ ______ ______ ____ ______ ________ _________ Adams {'Female'} false 66 137 8235 22.112 127 83 Alexander {'Male' } true 69 171 1300 25.252 128 99 Allen {'Female'} false 63 143 7432 25.331 113 80 Anderson {'Female'} false 68 128 1577 19.462 114 77 Bailey {'Female'} false 68 130 2239 19.766 113 81

Create aBloodPressurevariable to hold blood pressure readings in a 100-by-2 table variable.

T.BloodPressure = [T.Systolic T.Diastolic];

DeleteSystolicandDiastolicfrom the table since they are redundant.

T.Systolic = [];T.Diastolic = [];T(1:5,:)

ans=5×7 table Gender Smoker Height Weight ID BMI BloodPressure __________ ______ ______ ______ ____ ______ _____________ Adams {'Female'} false 66 137 8235 22.112 127 83 Alexander {'Male' } true 69 171 1300 25.252 128 99 Allen {'Female'} false 63 143 7432 25.331 113 80 Anderson {'Female'} false 68 128 1577 19.462 114 77 Bailey {'Female'} false 68 130 2239 19.766 113 81

To putIDas the first column, reorder the table variables by position.

T = T(:,[5 1:4 6 7]);T(1:5,:)

ans=5×7 table ID Gender Smoker Height Weight BMI BloodPressure ____ __________ ______ ______ ______ ______ _____________ Adams 8235 {'Female'} false 66 137 22.112 127 83 Alexander 1300 {'Male' } true 69 171 25.252 128 99 Allen 7432 {'Female'} false 63 143 25.331 113 80 Anderson 1577 {'Female'} false 68 128 19.462 114 77 Bailey 2239 {'Female'} false 68 130 19.766 113 81

You also can reorder table variables by name. To reorder the table variables so thatGenderis last:

Find'Gender'in theVariableNamesproperty of the table.
Move'Gender'to the end of a cell array of variable names.
Use the cell array of names to reorder the table variables.

varnames = T.Properties.VariableNames;others = ~strcmp('Gender',varnames);varnames = [varnames(others) 'Gender'];T = T(:,varnames);

Display the first five rows of the reordered table.

T(1:5,:)

ans=5×7 table ID Smoker Height Weight BMI BloodPressure Gender ____ ______ ______ ______ ______ _____________ __________ Adams 8235 false 66 137 22.112 127 83 {'Female'} Alexander 1300 true 69 171 25.252 128 99 {'Male' } Allen 7432 false 63 143 25.331 113 80 {'Female'} Anderson 1577 false 68 128 19.462 114 77 {'Female'} Bailey 2239 false 68 130 19.766 113 81 {'Female'}

Write Table to File

You can write the entire table to a file, or create a subtable to write a selected portion of the original table to a separate file.

WriteTto a file with thewritetablefunction.

writetable(T,'allPatientsBMI.txt');

You can use thereadtablefunction to read the data inallPatientsBMI.txtinto a new table.

Create a subtable and write the subtable to a separate file. Delete the rows that contain data on patients who are smokers. Then remove theSmokervariable.nonsmokerscontains data only for the patients who are not smokers.

nonsmokers = T;toDelete = (nonsmokers.Smoker == true);nonsmokers(toDelete,:) = [];nonsmokers.Smoker = [];

Writenonsmokersto a file.

writetable(nonsmokers,'nonsmokersBMI.txt');