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Find groups and return group numbers

`G = findgroups(A)`

`G = findgroups(A1,...,AN)`

```
[G,ID] =
findgroups(A)
```

`[G,ID1,...,IDN] = findgroups(A1,...,AN)`

`G = findgroups(T)`

```
[G,TID]
= findgroups(T)
```

returns `G`

= findgroups(`A`

)`G`

,
a vector of group numbers created from the grouping variable `A`

.
The output argument `G`

contains integer values from
1 to `N`

, indicating `N`

distinct
groups for the `N`

unique values in `A`

.
For example, if `A`

is `{'b','a','a','b'}`

,
then `findgroups`

returns `G`

as ```
[2
1 1 2]
```

. You can use `G`

to split groups
of data out of other variables. Use `G`

as an input
argument to `splitapply`

in the Split-Apply-Combine Workflow.

`findgroups`

treats empty character vectors
and `NaN`

, `NaT`

, and undefined
categorical values in `A`

as missing values and returns `NaN`

as
the corresponding elements of `G`

.

creates
group numbers from `G`

= findgroups(A1,...,AN)`A1,...,AN`

. The `findgroups`

function
defines groups as the unique combinations of values across `A1,...,AN`

.
For example, if `A1`

is `{'a','a','b','b'}`

and `A2`

is ```
[0
1 0 0]
```

, then `findgroups(A1,A2)`

returns `G`

as ```
[1
2 3 3]
```

, because the combination `'b' 0`

occurs
twice.

`[`

also
returns the unique values for each group across `G`

,ID1,...,IDN] = findgroups(A1,...,AN)`ID1,...,IDN`

.
The values across `ID1,...,IDN`

define the groups.
For example, if `A1`

is `{'a','a','b','b'}`

and `A2`

is ```
[0
1 0 0]
```

, then `findgroups(A1,A2)`

returns `G`

as ```
[1
2 3 3]
```

, and `ID1`

and `ID2`

as `{'a','a','b'}`

and ```
[0
1 0]
```

.

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