The walk activity entails participants walking in a straight line for approximately 20 steps with the mobile device in their pocket or in a bag.
walk_data
A 3002 x 6 data frame with column names attitude,
timestamp, rotationRate, userAcceleration,
gravity, and magneticField. The column names correspond
to the measurements returned by a
[CMDeviceMotion](https://developer.apple.com/documentation/coremotion/cmdevicemotion)
object as described in Apple's developer documentation. rotationRate,
userAcceleration,gravity are each 3002 x 3 data frames with column names
x, y, z containing axial measurements for their respective sensor.
magneticField has an additional column accuracy specifying
the calibration accuracy of the magnetic field estimate. attitude
columns are quaternion coefficients.