cumulativeEnrollment = data
.map(d => immutable.Map()
.set('timestamp', d.get('timestamp'))
.set('value', {'enroll': 1, 'unenroll': -1}[d.get('event_method')]))
.reduce(
(acc, d) => acc.push(d.set('value', acc.getIn([acc.size - 1, 'value'], 0) + d.get('value', 0))),
immutable.List()
)
.toJS()