# Add a cumulative membership effect to a `data.frame`

Source: `R/model-design-tools.R`

`enw_add_cumulative_membership.Rd`

This function adds a cumulative membership effect to a data
frame. This is useful for specifying models such as random walks (using
`rw()`

) where these features can be used in the design matrix with the
appropriate formula. Supports grouping via the optional `.group`

column.
Note that cumulative membership is indexed to start with zero (i.e. the
first observation is assigned a cumulative membership of zero).

## Value

A `data.frame`

with a new columns `cfeature$`

that contain the
cumulative membership effect for each value of `feature`

. For example if the
original `feature`

was `week`

(with numeric entries `1, 2, 3`

) then the new
columns will be `cweek1`

, `cweek2`

, and `cweek3`

.

## See also

Functions used to formulate models
`enw_add_pooling_effect()`

,
`enw_design()`

,
`enw_effects_metadata()`

,
`enw_one_hot_encode_feature()`

## Examples

```
metaobs <- data.frame(week = 1:2)
enw_add_cumulative_membership(metaobs, "week")
#> week .group cweek2
#> <int> <num> <num>
#> 1: 1 1 0
#> 2: 2 1 1
metaobs <- data.frame(week = 1:3, .group = c(1,1,2))
enw_add_cumulative_membership(metaobs, "week")
#> week .group cweek2 cweek3
#> <int> <num> <num> <num>
#> 1: 1 1 0 0
#> 2: 2 1 1 0
#> 3: 3 2 0 1
```