Adding a column of the same character name for all the rows in a table

I have a table in MATLAB that I'd like to add a column that contains a character variable that's the same throughout the column, but different size lengths. Here's a code for two random tables.

Is there a way, for example, for me to add a column named 'Time' that contains the character 'hours' for both based on the number of rows of the table?

r1 = rand(100,1);
r1 = array2table(r1);
r1.Properties.VariableNames = {'Random1'};

r2 = rand(54,1);
r2 = array2table(r2);
r2.Properties.VariableNames = {'Random2'};

[Abhishek Gupta]

Hi,

As per my understanding, you want to add a column to the existing table. You can do the same in the following way: -

r1 = rand(100,1);
r1 = array2table(r1);
r1.Properties.VariableNames = {'Random1'};
strs1 = repmat('hours', size(r1, 1), 1);         
vTbl1 = table(strs1, 'VariableNames',{'Time'});
r1 = [r1, vTbl1];

r2 = rand(54,1);
r2 = array2table(r2);
r2.Properties.VariableNames = {'Random2'};
strs2 = repmat('hours', size(r2, 1), 1);         
vTbl2 = table(strs2, 'VariableNames',{'Time'});
r2 = [r2, vTbl2];

Answer 1

[Scott MacKenzie]

From my understanding of the question, this is simply a matter of making the necessary assignment to r1.Time or r2.Time. Do so and a new column with variable name Time is automatically appended to the table:

r1 = rand(100,1);
r1 = array2table(r1);
r1.Properties.VariableNames = {'Random1'};
r1.Time = repmat({'hours'}, height(r1), 1);

r2 = rand(54,1);
r2 = array2table(r2);
r2.Properties.VariableNames = {'Random2'};
r2.Time = repmat({'hours'}, height(r2), 1);

Here's a command-window dump of the first 8 rows in the new r1:

>> head(r1)

ans =

8×2 table

Random1 Time

_________ _________

0.49707 {'hours'}

0.32079 {'hours'}

0.61628 {'hours'}

0.0068941 {'hours'}

0.062934 {'hours'}

0.92002 {'hours'}

0.90616 {'hours'}

0.83154 {'hours'}

Answer 2

[Peter Perkins]

It's even simpler than that:

>> r1 = array2table(rand(5,1),'VariableNames',"Random1");
>> r1.Time(:) = "hours"
r1 =
5×2 table
Random1     Time  
_______    _______
0.31907    "hours"
0.98605    "hours"
0.71818    "hours"
0.41318    "hours"
0.09863    "hours"

It's not clear what you would do with this variable, though. I'm gonna take a guess that at some point you will end up vertically concatenating these tables and the text will be different in different tables (except right now, you can't because your var names are different). In that case, use categorical, not text.

>> r1 = array2table(rand(2,1),'VariableNames',"X");
>> r1.Time(:) = categorical("hours")
r1 =
  2×2 table
       X       Time 
    _______    _____
    0.73456    hours
    0.63731    hours
>> r2 = array2table(rand(3,1),'VariableNames',"X");
>> r2.Time(:) = categorical("days")
r2 =
  3×2 table
       X        Time
    ________    ____
    0.073842    days
     0.12051    days
      0.9816    days
>> [r1; r2]
ans =
  5×2 table
       X        Time 
    ________    _____
     0.73456    hours
     0.63731    hours
    0.073842    days 
     0.12051    days 
      0.9816    days