stack - Class: dataset

Stack data from multiple variables into single variable

Syntax

tall = stack(wide,datavar) [tall,iwide] = stack(wide,datavar) tall = stack(wide,datavar,Parameter,value)

Description

tall = stack(wide,datavar) converts a wide-format dataset array into a tall-format array, by stacking multiple variables in wide into a single variable in tall. In general, tall contains fewer variables but more observations than wide.

datavar specifies a group of m data variables in wide. stack creates a single data variable in tall by interleaving their values, and if wide has n observations, then tall has m-by-n observations. In other words, stack takes the m data values from each observation in wide and stacks them up to create m observations in tall. datavar is a positive integer, a vector of positive integers, a variable name, a cell array containing one or more variable names, or a logical vector. stack also creates a grouping variable in tall to indicate which of the m data variables in wide each observation in tall corresponds to.

stack copies the remaining variables from wide to tall without stacking, by replicating each of their values m times. These variables are typically grouping variables. Because their values are constant across each group of m observations in tall, they identify which observation in wide an observation in tall came from.

[tall,iwide] = stack(wide,datavar) returns an index vector iwide indicating the correspondence between observations in tall and those in wide. stack creates tall(j,:) using wide(iwide(j),datavars).

For more information on grouping variables, see Grouping Variables.

Inputs

tall = stack(wide,datavar,Parameter,value) uses the following parameter name/value pairs to control how stack converts variables in wide to variables in tall:

`'ConstVars'`	Variables in `wide` to copy to `tall` without stacking. `ConstVars` is a positive integer, a vector of positive integers, a variable name, a cell array containing one or more variable names, or a logical vector. The default is all variables in `wide` not specified in `datavar`.
`'NewDataVarName'`	A name for the data variable to be created in `tall`. The default is a concatenation of the names of the `m` variables that are stacked up.
`'DataIndVarName'`	A name for the grouping variable to create in `tall` to indicate the source of each value in the new data variable. The default is based on the `'NewDataVarNames'` parameter.

You can also specify multiple groups of data variables in wide, each of which becomes a variable in tall. All groups must contain the same number of variables. Use a cell array to contain multiple parameter values for datavar, and a cell array of strings to contain multiple 'NewDataVarNames'.

Examples

Convert a wide format data set to tall format, and then back to a different wide format:

load flu
flu2 = stack(flu, 2:11, 'NewDataVarName','FluRate',...
'IndVarName','Region')
dateNames = cellstr(datestr(flu.Date,'mmm_DD_YYYY'));
flu3 = unstack(flu2, 'FluRate', 'Date',...
'NewDataVarNames',dateNames)