CodeBook.md

Code book for the tidy data set produced by run_analysis.R

This code book documents the variables in the tidy data set (tidy_data_2.txt) produced by run_analysis.R. The data are averages and not raw measurements. For each variable, a description, its unit and its range are provided. There are additional notes and references at the end of this document.

The variable names have been named according to the original data set [1] with just the addition of an avg- prefix. This is done to ensure a 1-to-1 correspondence with the analysis of other users of the data set, assuming of course that they also keep the original variable names.

Abbreviations

• Acc: accelerometer
• avg: average
• Gyro: gyroscope
• Mag: magnitude
• std: standard deviation

Prefixes

• f: frequency
• t: time

Table of variables

The ranges of the original variables except subject and activity have been normalized to [-1, 1] and thus by dimensional analysis the numeric variables in this table have no unit. The subject and activity variables also have no unit because they are nominal variables.

Num	Name	Description	Unit	Range
1	subject	The id of the subject doing the activity.	No unit	1 - 30
2	activity	The activity itself.	No unit	LAYING | SITTING | STANDING | WALKING | WALKING_DOWNSTAIRS | WALKING_UPSTAIRS
3	avg-tBodyAcc-mean()-X	Average of the means of body acceleration in the X-axis (time domain).	No unit	[-1, 1]
4	avg-tBodyAcc-mean()-Y	Average of the means of body acceleration in the Y-axis (time domain).	No unit	[-1, 1]
5	avg-tBodyAcc-mean()-Z	Average of the means of body acceleration in the Z-axis (time domain).	No unit	[-1, 1]
6	avg-tBodyAcc-std()-X	Average of the standard deviations of body acceleration in the X-axis (time domain).	No unit	[-1, 1]
7	avg-tBodyAcc-std()-Y	Average of the standard deviations of body acceleration in the Y-axis (time domain).	No unit	[-1, 1]
8	avg-tBodyAcc-std()-Z	Average of the standard deviations of body acceleration in the Z-axis (time domain).	No unit	[-1, 1]
9	avg-tGravityAcc-mean()-X	Average of the means of gravitational acceleration in the X-axis (time domain).	No unit	[-1, 1]
10	avg-tGravityAcc-mean()-Y	Average of the means of gravitational acceleration in the Y-axis (time domain).	No unit	[-1, 1]
11	avg-tGravityAcc-mean()-Z	Average of the means of gravitational acceleration in the Z-axis (time domain).	No unit	[-1, 1]
12	avg-tGravityAcc-std()-X	Average of the standard deviations of gravitational acceleration in the X-axis (time domain).	No unit	[-1, 1]
13	avg-tGravityAcc-std()-Y	Average of the standard deviations of gravitational acceleration in the Y-axis (time domain).	No unit	[-1, 1]
14	avg-tGravityAcc-std()-Z	Average of the standard deviations of gravitational acceleration in the Z-axis (time domain).	No unit	[-1, 1]
15	avg-tBodyAccJerk-mean()-X	Average of the means of body jerk in the X-axis (time domain).	No unit	[-1, 1]
16	avg-tBodyAccJerk-mean()-Y	Average of the means of body jerk in the Y-axis (time domain).	No unit	[-1, 1]
17	avg-tBodyAccJerk-mean()-Z	Average of the means of body jerk in the Z-axis (time domain).	No unit	[-1, 1]
18	avg-tBodyAccJerk-std()-X	Average of the standard deviations of body jerk in the X-axis (time domain).	No unit	[-1, 1]
19	avg-tBodyAccJerk-std()-Y	Average of the standard deviations of body jerk in the Y-axis (time domain).	No unit	[-1, 1]
20	avg-tBodyAccJerk-std()-Z	Average of the standard deviations of body jerk in the Z-axis (time domain).	No unit	[-1, 1]
21	avg-tBodyGyro-mean()-X	Average of the means of body angular velocity in the X-axis (time domain).	No unit	[-1, 1]
22	avg-tBodyGyro-mean()-Y	Average of the means of body angular velocity in the Y-axis (time domain).	No unit	[-1, 1]
23	avg-tBodyGyro-mean()-Z	Average of the means of body angular velocity in the Z-axis (time domain).	No unit	[-1, 1]
24	avg-tBodyGyro-std()-X	Average of the standard deviations of body angular velocity in the X-axis (time domain).	No unit	[-1, 1]
25	avg-tBodyGyro-std()-Y	Average of the standard deviations of body angular velocity in the Y-axis (time domain).	No unit	[-1, 1]
26	avg-tBodyGyro-std()-Z	Average of the standard deviations of body angular velocity in the Z-axis (time domain).	No unit	[-1, 1]
27	avg-tBodyGyroJerk-mean()-X	Average of the means of body angular jerk in the X-axis (time domain).	No unit	[-1, 1]
28	avg-tBodyGyroJerk-mean()-Y	Average of the means of body angular jerk in the Y-axis (time domain).	No unit	[-1, 1]
29	avg-tBodyGyroJerk-mean()-Z	Average of the means of body angular jerk in the Z-axis (time domain).	No unit	[-1, 1]
30	avg-tBodyGyroJerk-std()-X	Average of the standard deviations of body angular jerk in the X-axis (time domain).	No unit	[-1, 1]
31	avg-tBodyGyroJerk-std()-Y	Average of the standard deviations of body angular jerk in the Y-axis (time domain).	No unit	[-1, 1]
32	avg-tBodyGyroJerk-std()-Z	Average of the standard deviations of body angular jerk in the Z-axis (time domain).	No unit	[-1, 1]
33	avg-tBodyAccMag-mean()	Average of the means of body acceleration magnitudes (time domain).	No unit	[-1, 1]
34	avg-tBodyAccMag-std()	Average of the standard deviations of body acceleration magnitudes (time domain).	No unit	[-1, 1]
35	avg-tGravityAccMag-mean()	Average of the means of gravitational acceleration magnitudes (time domain).	No unit	[-1, 1]
36	avg-tGravityAccMag-std()	Average of the standard deviations of gravitational acceleration magnitudes (time domain).	No unit	[-1, 1]
37	avg-tBodyAccJerkMag-mean()	Average of the means of body jerk magnitudes (time domain).	No unit	[-1, 1]
38	avg-tBodyAccJerkMag-std()	Average of the standard deviations of body jerk magnitudes (time domain).	No unit	[-1, 1]
39	avg-tBodyGyroMag-mean()	Average of the means of body angular velocity magnitudes (time domain).	No unit	[-1, 1]
40	avg-tBodyGyroMag-std()	Average of the standard deviations of body angular velocity magnitudes (time domain).	No unit	[-1, 1]
41	avg-tBodyGyroJerkMag-mean()	Average of the means of body angular jerk magnitudes (time domain).	No unit	[-1, 1]
42	avg-tBodyGyroJerkMag-std()	Average of the standard deviations of body angular jerk magnitudes (time domain).	No unit	[-1, 1]
43	avg-fBodyAcc-mean()-X	Average of the means of body acceleration in the X-axis (frequency domain).	No unit	[-1, 1]
44	avg-fBodyAcc-mean()-Y	Average of the means of body acceleration in the Y-axis (frequency domain).	No unit	[-1, 1]
45	avg-fBodyAcc-mean()-Z	Average of the means of body acceleration in the Z-axis (frequency domain).	No unit	[-1, 1]
46	avg-fBodyAcc-std()-X	Average of the standard deviations of body acceleration in the X-axis (frequency domain).	No unit	[-1, 1]
47	avg-fBodyAcc-std()-Y	Average of the standard deviations of body acceleration in the Y-axis (frequency domain).	No unit	[-1, 1]
48	avg-fBodyAcc-std()-Z	Average of the standard deviations of body acceleration in the Z-axis (frequency domain).	No unit	[-1, 1]
49	avg-fBodyAccJerk-mean()-X	Average of the means of body jerk in the X-axis (frequency domain).	No unit	[-1, 1]
50	avg-fBodyAccJerk-mean()-Y	Average of the means of body jerk in the Y-axis (frequency domain).	No unit	[-1, 1]
51	avg-fBodyAccJerk-mean()-Z	Average of the means of body jerk in the Z-axis (frequency domain).	No unit	[-1, 1]
52	avg-fBodyAccJerk-std()-X	Average of the standard deviations of body jerk in the X-axis (frequency domain).	No unit	[-1, 1]
53	avg-fBodyAccJerk-std()-Y	Average of the standard deviations of body jerk in the Y-axis (frequency domain).	No unit	[-1, 1]
54	avg-fBodyAccJerk-std()-Z	Average of the standard deviations of body jerk in the Z-axis (frequency domain).	No unit	[-1, 1]
55	avg-fBodyGyro-mean()-X	Average of the means of body angular velocity in the X-axis (frequency domain).	No unit	[-1, 1]
56	avg-fBodyGyro-mean()-Y	Average of the means of body angular velocity in the Y-axis (frequency domain).	No unit	[-1, 1]
57	avg-fBodyGyro-mean()-Z	Average of the means of body angular velocity in the Z-axis (frequency domain).	No unit	[-1, 1]
58	avg-fBodyGyro-std()-X	Average of the standard deviations of body angular velocity in the X-axis (frequency domain).	No unit	[-1, 1]
59	avg-fBodyGyro-std()-Y	Average of the standard deviations of body angular velocity in the Y-axis (frequency domain).	No unit	[-1, 1]
60	avg-fBodyGyro-std()-Z	Average of the standard deviations of body angular velocity in the Z-axis (frequency domain).	No unit	[-1, 1]
61	avg-fBodyAccMag-mean()	Average of the means of body acceleration magnitudes (frequency domain).	No unit	[-1, 1]
62	avg-fBodyAccMag-std()	Average of the standard deviations of body acceleration magnitudes (frequency domain).	No unit	[-1, 1]
63	avg-fBodyBodyAccJerkMag-mean()	Average of the means of body jerk magnitudes (frequency domain).	No unit	[-1, 1]
64	avg-fBodyBodyAccJerkMag-std()	Average of the standard deviations of body jerk magnitudes (frequency domain).	No unit	[-1, 1]
65	avg-fBodyBodyGyroMag-mean()	Average of the means of body angular velocity magnitudes (frequency domain).	No unit	[-1, 1]
66	avg-fBodyBodyGyroMag-std()	Average of the standard deviations of body angular velocity magnitudes (frequency domain).	No unit	[-1, 1]
67	avg-fBodyBodyGyroJerkMag-mean()	Average of the means of body angular jerk magnitudes (frequency domain).	No unit	[-1, 1]
68	avg-fBodyBodyGyroJerkMag-std()	Average of the standard deviations of body angular jerk magnitudes (frequency domain).	No unit	[-1, 1]

Notes

• There are variable names with BodyBody in them. These appear to be typos, carried over from the original data set.
• Jerk is the rate of change of acceleration, or the derivative of acceleration with respect to time (from Wikipedia [2]).
• The derivative of angular velocity with respect to time is angular acceleration and not angular jerk. Thus, it appears that any occurance of GyroJerk in the variable names above should be replaced with perhaps GyroAccln. This claim has support from the data set paper itself (see Table 2 of [1]) but it's best to have confirmation from the data set authors.

References

[1] Davide Anguita, Alessandro Ghio, Luca Oneto, Xavier Parra and Jorge L. Reyes-Ortiz (2013). "A Public Domain Dataset for Human Activity Recognition Using Smartphones". 21th European Symposium on Artificial Neural Networks, Computational Intelligence and Machine Learning, ESANN 2013. Bruges, Belgium.

[2] Wikipedia (2015). "Jerk (physics)". https://en.wikipedia.org/wiki/Jerk_(physics) Accessed on 24 July 2015.