MATLAB: Containers.Map how to set keys and values

containerindexkeysmapmappingmatchvalues

Hello, so I want to create a Containers.Map. However, I am unsure of how to create it as the data that I want to use as key values is embedded in a cell array. For example, the cell array is 15×1 and looks like this: [1501×15 table, 1501×15 table….etc]I want to create a containers map that uses the 6th column of EACH table as the key values and the 8th column as the pairing values. How do I go about doing this?

Best Answer

Hi Xander,

I am assuming that you already have a cell array which contains tables as cells.

For this example we will consider the following structure:

TableName T1 ; Columns: Age,Height,Weight,BloodPressure,LastName

TableName T2 ; Columns: Age,Height,Weight,BloodPressure,LastName

CellArray tableAsCells; Rows: T1; T2

Step 1: Fetch a Table from the cell array :

>> grabATable = tableAsCells{1};

Step 2: Fetch columns from the table that you want to keep as keys:

>> keySets = table2cell(grabATable(:,5));

The function "table2cell" will convert the 5th column of the table elements into a cell array , which will act as our keys in the container.Map object.

Step 3: Fetch column from the table to be the values:

>> valueSets = table2cell(grabATable(:,3));

The function "table2array" will convert the 5th column of the table elements into a cell , which will act as our values in the container.Map object. NOTE: We could also use "table2array" function here.

Step 4: Put the keySets and valueSets in a container.Map object:

>> mapObj = containers.Map(keySets,valueSets);

Step 5: Fetching values form the map.

>> mapObj('Any_Key_From_keySets_cell_array');

For Example:

>> mapObj('Williams');

More information on "table2cell" , "table2array" and "containers.Map" can be found in the documentation links below:

table2cell Function MATLAB

table2array Function MATLAB

container.Map class MATLAB

Note: If you have to append in the map, if can be only done column wise.

I have attached a sample code to try this.

Hope this helps.

Thanks

Sudhanshu Bhatt

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MATLAB: Using a containers.Map to find values

Hi Xander,

I am assuming that you have the data you want to insert into the table as 7th column.

For this example we will consider the following structure:

TableName T1 ; Columns: Age,Height,Weight,BloodPressure,LastName

TableName T2 ; Columns: Age,Height,Weight,BloodPressure,LastName

CellArray tableAsCells; Rows: (Table T1); (Table T2)

NewColumn Smoker: {'Yes';'Yes';'Yes';'No';'No'};

There are two approaches to adding a column to an existing table as listed below:

Approach 1: Appending the new column to the pre-existing table:

Step 1: Fetch a Table from the cell array :

>> grabATable = tableAsCells{1};

Step 2: Add column to this table :

>> T1 = [T1, Smoker];
>> T1.Properties.VariableNames(6) = {'Smoker'};

Approach 2: Creating a temporary table and concatenating it to the original table :

Step 1: Fetch a Table from the cell array :

>> grabATable = tableAsCells{1};

Step 2: Add column to this table :

>> newTable = table(Smoker);
>> T1 = [T1,newTable];

Below are the steps to add key and value objects to the Existing container.Map object:

Step 1: Creating new key and Value pairs :

>> newKeyValueSets = {'PlaceHolder1', 'PlaceHolder2', 'PlaceHodler3', 'PlaceHoler4' };
>> newValueSets = {100,110,120,130};

Step 2: Creating a new Map object :

>> newMapObj = containers.Map(newKeyValueSets,newValueSets);

Step 3: Concatenate the two map objects into the original object :

>> mapObj = [mapObj; newMapObj];

More information on concatenating values to map objects can be found in the documentation link below:

Concatenating into container.Map Objects

Hope this helps.

Thanks

Sudhanshu Bhatt

Best Answer

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MATLAB: Using a containers.Map to find values

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