I am having trouble understanding this error "To assign to or create a variable in a table, the number of rows must match the height of the table.", can someone explain?

As stated in the title, I'm struggling with getting rid of error message "To assign to or create a variable in a table, the number of rows must match the height of the table."

Here is a snippit of my original code. The line specifically causing hte probled is the line within the For loop. Sorry if this is a simple question, I do not usually work MATLAB and got thrown into this project. Thank you!

units_tbl(1,:)
values_tbl_new = vertcat(units_tbl(1,:),values_tbl);
for k = 1:length(vars_wanted)
    values_tbl_new.(vars_wanted(k)) = values_tbl.(vars_wanted(k));
end

[Stephen23]

"I am having trouble understanding this error "To assign to or create a variable in a table, the number of rows must match the height of the table.", can someone explain?"

Here is a table with three rows:

T = array2table(randi(9,3,4))

T = 3x4 table
    Var1    Var2    Var3    Var4
    ____    ____    ____    ____

     9       2       5       6  
     4       1       8       6  
     5       4       8       7  

Creating a new column/variable which also has three rows will work correctly:

T.('new') = [1;99;Inf]

T = 3x5 table
    Var1    Var2    Var3    Var4    new
    ____    ____    ____    ____    ___

     9       2       5       6        1
     4       1       8       6       99
     5       4       8       7      Inf

Creating a new column/variable which does not have three rows will fail:

T.('bad') = [1;2;3;4;5;6]

Error using . (line 507)
To assign to or create a variable in a table, the number of rows must match the height of the table.

Answer 1

[Cris LaPierre]

Values_tbl_new has n+1 rows because you vertically concatenate the first row of units_tbl to values_tbl.

You then try to assign one column (or variable) of table values_tbl to a colum (or variable) of values_tbl_new. The number of rows differ between these two tables by 1, hence the error.

I would suggest not placing your units in the first row. Instead, add it to the table properties. The VariableUnits one would make sense to me.

That might look like this.

values_tbl_new = table();
values_tbl_nes.Properties.VariableUnits = units_tbl(1,:);
for k = 1:length(vars_wanted)
    values_tbl_new.(vars_wanted(k)) = values_tbl.(vars_wanted(k));
end

[Cris LaPierre]

Here's an example of how I would do it.

values_tbl = readtable('patients.xls')

values_tbl = 100x10 table
      LastName        Gender      Age              Location               Height    Weight    Smoker    Systolic    Diastolic    SelfAssessedHealthStatus
    ____________    __________    ___    _____________________________    ______    ______    ______    ________    _________    ________________________

    {'Smith'   }    {'Male'  }    38     {'County General Hospital'  }      71       176      true        124          93             {'Excellent'}      
    {'Johnson' }    {'Male'  }    43     {'VA Hospital'              }      69       163      false       109          77             {'Fair'     }      
    {'Williams'}    {'Female'}    38     {'St. Mary's Medical Center'}      64       131      false       125          83             {'Good'     }      
    {'Jones'   }    {'Female'}    40     {'VA Hospital'              }      67       133      false       117          75             {'Fair'     }      
    {'Brown'   }    {'Female'}    49     {'County General Hospital'  }      64       119      false       122          80             {'Good'     }      
    {'Davis'   }    {'Female'}    46     {'St. Mary's Medical Center'}      68       142      false       121          70             {'Good'     }      
    {'Miller'  }    {'Female'}    33     {'VA Hospital'              }      64       142      true        130          88             {'Good'     }      
    {'Wilson'  }    {'Male'  }    40     {'VA Hospital'              }      68       180      false       115          82             {'Good'     }      
    {'Moore'   }    {'Male'  }    28     {'St. Mary's Medical Center'}      68       183      false       115          78             {'Excellent'}      
    {'Taylor'  }    {'Female'}    31     {'County General Hospital'  }      66       132      false       118          86             {'Excellent'}      
    {'Anderson'}    {'Female'}    45     {'County General Hospital'  }      68       128      false       114          77             {'Excellent'}      
    {'Thomas'  }    {'Female'}    42     {'St. Mary's Medical Center'}      66       137      false       115          68             {'Poor'     }      
    {'Jackson' }    {'Male'  }    25     {'VA Hospital'              }      71       174      false       127          74             {'Poor'     }      
    {'White'   }    {'Male'  }    39     {'VA Hospital'              }      72       202      true        130          95             {'Excellent'}      
    {'Harris'  }    {'Female'}    36     {'St. Mary's Medical Center'}      65       129      false       114          79             {'Good'     }      
    {'Martin'  }    {'Male'  }    48     {'VA Hospital'              }      71       181      true        130          92             {'Good'     }      

vars_wanted = ["Height" "Weight" "Smoker"];
values_tbl_new = values_tbl(:,ismember(values_tbl.Properties.VariableNames,vars_wanted))

values_tbl_new = 100x3 table
    Height    Weight    Smoker
    ______    ______    ______

      71       176      true  
      69       163      false 
      64       131      false 
      67       133      false 
      64       119      false 
      68       142      false 
      64       142      true  
      68       180      false 
      68       183      false 
      66       132      false 
      68       128      false 
      66       137      false 
      71       174      false 
      72       202      true  
      65       129      false 
      71       181      true  

[Steven Lord]

Or even simpler, skip the ismember call and the direct request for the variable names from the table property. Just use indexing.

values_tbl = readtable('patients.xls');
head(values_tbl) % Show just the first few rows

      LastName        Gender      Age              Location               Height    Weight    Smoker    Systolic    Diastolic    SelfAssessedHealthStatus
    ____________    __________    ___    _____________________________    ______    ______    ______    ________    _________    ________________________

    {'Smith'   }    {'Male'  }    38     {'County General Hospital'  }      71       176      true        124          93             {'Excellent'}      
    {'Johnson' }    {'Male'  }    43     {'VA Hospital'              }      69       163      false       109          77             {'Fair'     }      
    {'Williams'}    {'Female'}    38     {'St. Mary's Medical Center'}      64       131      false       125          83             {'Good'     }      
    {'Jones'   }    {'Female'}    40     {'VA Hospital'              }      67       133      false       117          75             {'Fair'     }      
    {'Brown'   }    {'Female'}    49     {'County General Hospital'  }      64       119      false       122          80             {'Good'     }      
    {'Davis'   }    {'Female'}    46     {'St. Mary's Medical Center'}      68       142      false       121          70             {'Good'     }      
    {'Miller'  }    {'Female'}    33     {'VA Hospital'              }      64       142      true        130          88             {'Good'     }      
    {'Wilson'  }    {'Male'  }    40     {'VA Hospital'              }      68       180      false       115          82             {'Good'     }      

vars_wanted = ["Height" "Weight" "Smoker"];
values_tbl_new = values_tbl(:, vars_wanted); % Indexing using variable names
head(values_tbl_new) % Show just the first few rows

    Height    Weight    Smoker
    ______    ______    ______

      71       176      true  
      69       163      false 
      64       131      false 
      67       133      false 
      64       119      false 
      68       142      false 
      64       142      true  
      68       180      false 

See the "Index by Variable Names" section on this documentation page. The table at the end of that documentation page describes other techniques / syntaxes to access data in a table.