The file run_analysis.R is the code for run to obtain the data as an answer to the questions of the project.
The code starts settings some paths where the data is located.
It works in any location, just is the way you obtain the tree strucutre as you unzip the data zip file.
Then it reads all the data, in separate files, with the same names of the original data.
Then you can see that each section answers each question.
The code is documented where you can find the explanation for each command.
#------------------------------------------------------------------------------#
# 1. Merges the training and the test sets to create one data set.
#------------------------------------------------------------------------------#
#------------------------------------------------------------------------------#
# 2. Extracts only the measurements on the mean and
# standard deviation for each measurement.
#------------------------------------------------------------------------------#
#------------------------------------------------------------------------------#
# 3. Uses descriptive activity names to name the activities in the data set
#------------------------------------------------------------------------------#
#------------------------------------------------------------------------------#
# 4.Appropriately labels the data set with descriptive variable names.
#------------------------------------------------------------------------------#
#------------------------------------------------------------------------------#
# 5. From the data set in step 4, creates a second,
# independent tidy data set with the average of
# each variable for each activity and each subject.
#------------------------------------------------------------------------------#
- subject: Id of the suject in the experiment.
- activity: Label of the activity (Walking,Walking Upstairs,Walking Downstairs,Sitting,Standing,Laying).
The main variables are:
- BodyAccJerk
- BodyAccMag
- BodyAcc
- BodyBodyAccJerkMag
- BodyBodyGyroJerkMag
- BodyBodyGyroMag
- BodyGyro
As the original documentation says:
The features selected for this database come from the accelerometer and gyroscope 3-axial raw signals.
Again it says:
the acceleration signal was then separated into body and gravity acceleration signals.
But as the README file says:
Features are normalized and bounded within [-1,1].
So all values are dimensionless, asociated with acceleration signals and gyriscope 3-axial signals.
In this case the following are 3D thats the reason the have an X, Y and Z values.
- BodyAccJerk
- BodyAcc
- BodyGyro
All variables are in two group that starts with t or f, meaning that comes from time or frequency domain.
The variables with Mag sufix mean that is a 3D magnitud of the variable.
- BodyAccMag
- BodyBodyAccJerkMag
- BodyBodyGyroJerkMag
- BodyBodyGyroMag