head

Get top rows of table, timetable, or tall array

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Syntax

B = head(A)

B = head(A,k)

Description

example

B = head(A) returns the first eight rows of table or timetable A.

example

B = head(A,k) returns the first k rows of A.

Examples

collapse all

Preview Table

Open Live Script

Create a table that contains 100 rows and five variables.

load patients
T = table(LastName,Gender,Age,Height,Weight);
size(T)

ans = 1×2

   100     5

Preview the first eight rows.

T2 = head(T)

T2=8×5 table
      LastName        Gender      Age    Height    Weight
    ____________    __________    ___    ______    ______

    {'Smith'   }    {'Male'  }    38       71       176  
    {'Johnson' }    {'Male'  }    43       69       163  
    {'Williams'}    {'Female'}    38       64       131  
    {'Jones'   }    {'Female'}    40       67       133  
    {'Brown'   }    {'Female'}    49       64       119  
    {'Davis'   }    {'Female'}    46       68       142  
    {'Miller'  }    {'Female'}    33       64       142  
    {'Wilson'  }    {'Male'  }    40       68       180

Preview Contents of Tall Table

Open Live Script

Create a tall table and preview the first few rows of data.

Create a tall table for the airlinesmall.csv data set. Select a subset of the variables to work with. Use head to extract the first few rows of data.

varnames = {'Year','Month','ArrDelay','DepDelay','UniqueCarrier'};
ds = tabularTextDatastore('airlinesmall.csv','TreatAsMissing','NA',...
    'SelectedVariableNames',varnames);
T = tall(ds)

T =

  Mx5 tall table

    Year    Month    ArrDelay    DepDelay    UniqueCarrier
    ____    _____    ________    ________    _____________

    1987     10          8          12          {'PS'}    
    1987     10          8           1          {'PS'}    
    1987     10         21          20          {'PS'}    
    1987     10         13          12          {'PS'}    
    1987     10          4          -1          {'PS'}    
    1987     10         59          63          {'PS'}    
    1987     10          3          -2          {'PS'}    
    1987     10         11          -1          {'PS'}    
     :        :         :           :              :
     :        :         :           :              :

tt = head(T)

tt =

  8x5 tall table

    Year    Month    ArrDelay    DepDelay    UniqueCarrier
    ____    _____    ________    ________    _____________

    1987     10          8          12          {'PS'}    
    1987     10          8           1          {'PS'}    
    1987     10         21          20          {'PS'}    
    1987     10         13          12          {'PS'}    
    1987     10          4          -1          {'PS'}    
    1987     10         59          63          {'PS'}    
    1987     10          3          -2          {'PS'}    
    1987     10         11          -1          {'PS'}

Collect the results into memory to view the data.

t8 = gather(tt)

t8=8×5 table
    Year    Month    ArrDelay    DepDelay    UniqueCarrier
    ____    _____    ________    ________    _____________

    1987     10          8          12          {'PS'}    
    1987     10          8           1          {'PS'}    
    1987     10         21          20          {'PS'}    
    1987     10         13          12          {'PS'}    
    1987     10          4          -1          {'PS'}    
    1987     10         59          63          {'PS'}    
    1987     10          3          -2          {'PS'}    
    1987     10         11          -1          {'PS'}

Retrieve Specified Number of Rows in Tall Array

Open Live Script

Preview the first 20 rows of data in a tall table.

Create a tall table for the airlinesmall.csv data set. Select a subset of the variables to work with, and treat 'NA' values as missing data so that datastore replaces them with NaN values. Use head to view the first 20 rows of data.

varnames = {'Year','Month','ArrDelay','DepDelay','UniqueCarrier'};
ds = tabularTextDatastore('airlinesmall.csv','TreatAsMissing','NA',...
    'SelectedVariableNames',varnames);
T = tall(ds)

T =

  Mx5 tall table

    Year    Month    ArrDelay    DepDelay    UniqueCarrier
    ____    _____    ________    ________    _____________

    1987     10          8          12          {'PS'}    
    1987     10          8           1          {'PS'}    
    1987     10         21          20          {'PS'}    
    1987     10         13          12          {'PS'}    
    1987     10          4          -1          {'PS'}    
    1987     10         59          63          {'PS'}    
    1987     10          3          -2          {'PS'}    
    1987     10         11          -1          {'PS'}    
     :        :         :           :              :
     :        :         :           :              :

tt = head(T,20)

tt =

  20x5 tall table

    Year    Month    ArrDelay    DepDelay    UniqueCarrier
    ____    _____    ________    ________    _____________

    1987     10          8          12          {'PS'}    
    1987     10          8           1          {'PS'}    
    1987     10         21          20          {'PS'}    
    1987     10         13          12          {'PS'}    
    1987     10          4          -1          {'PS'}    
    1987     10         59          63          {'PS'}    
    1987     10          3          -2          {'PS'}    
    1987     10         11          -1          {'PS'}    
     :        :         :           :              :
     :        :         :           :              :

Collect the results into memory to view the data.

t20 = gather(tt)

t20=20×5 table
    Year    Month    ArrDelay    DepDelay    UniqueCarrier
    ____    _____    ________    ________    _____________

    1987     10          8          12          {'PS'}    
    1987     10          8           1          {'PS'}    
    1987     10         21          20          {'PS'}    
    1987     10         13          12          {'PS'}    
    1987     10          4          -1          {'PS'}    
    1987     10         59          63          {'PS'}    
    1987     10          3          -2          {'PS'}    
    1987     10         11          -1          {'PS'}    
    1987     10          3           3          {'PS'}    
    1987     10          2           1          {'PS'}    
    1987     10         16          15          {'PS'}    
    1987     10          3           9          {'PS'}    
    1987     10         39          15          {'PS'}    
    1987     10         57          32          {'TW'}    
    1987     10          0          -3          {'TW'}    
    1987     10        -14           0          {'TW'}    
      ⋮

Input Arguments

collapse all

`A` — Input array
table | timetable

Input array, specified as a table or timetable.

Data Types: table | timetable

`k` — Number of rows to extract
scalar

Number of rows to extract, specified as a positive scalar integer. If A has fewer than k rows, then head returns all of A.

Output Arguments

collapse all

`B` — Requested rows
table | timetable

Requested rows, returned as a table or timetable. The data type of B is the same as A.

Extended Capabilities

Tall Arrays
Calculate with arrays that have more rows than fit in memory.

This function fully supports tall arrays. For more information, see Tall Arrays.

You can use head and tail with tall arrays of any valid underlying data type (single, double, int8, datetime, table, and so on).

If you are unsure whether the result returned by gather(A) will fit in memory, then use gather(head(A)) or gather(tail(A)). These commands still fully evaluate the tall array A, but only return a small subset of the result in memory.

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

This function fully supports GPU arrays. For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Distributed Arrays
Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

This function fully supports distributed arrays. For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).

Documentation

head

Syntax

Description

Examples

Preview Table

Preview Contents of Tall Table

Retrieve Specified Number of Rows in Tall Array

Input Arguments

`A` — Input array
table | timetable

`k` — Number of rows to extract
scalar

Output Arguments

`B` — Requested rows
table | timetable

Extended Capabilities

Tall Arrays
Calculate with arrays that have more rows than fit in memory.

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Distributed Arrays
Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

See Also

Topics

MATLAB Documentation

Support

Documentation

head

Syntax

Description

Examples

Preview Table

Preview Contents of Tall Table

Retrieve Specified Number of Rows in Tall Array

Input Arguments

A — Input array table | timetable

k — Number of rows to extract scalar

Output Arguments

B — Requested rows table | timetable

Extended Capabilities

Tall Arrays Calculate with arrays that have more rows than fit in memory.

GPU Arrays Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Distributed Arrays Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

See Also

Topics

MATLAB Documentation

Support

`A` — Input array
table | timetable

`k` — Number of rows to extract
scalar

`B` — Requested rows
table | timetable

Tall Arrays
Calculate with arrays that have more rows than fit in memory.

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Distributed Arrays
Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.