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Code Book for Getting and Cleaning Data - Course Project

Dataset description and cleaning

All original data were extracted to the ./data/UCI HAR Dataset folder, relative to the working directory of the analysis. All of the steps described below were run by the run_analysis.R script, as instructed by ReadMe.

The test and train sets for the activities were merged. I chose to leave the inertial signals data out, and only use the calculated data for the features (contained in the X_train.txt and X_test.txt files).

The X files contain data for 561 features (one in each column), where each row represents an individual and an activity (they may be repeated). The subject_test.txt and subject_train.txt files contain the same number of rows of the corresponding X file, each row containing one column meaning the ID for the subject which undertook an activity. Along the same lines, the y_test.txt and y_train.txt files contain the ID for the corresponding activity. The activity_labels.txt file matches the activity ID with the activity name, and the features.txt file matches the 561 features columns with their names.

The test and train data were then all merged, and a dataset with 10299 rows containing the subjects ID, activity names and the features together was created. Then, I begun my analysis. I picked from my data only the features with mean and standard deviation measures, and only the time-domain features (so, the frequency-domain ones were left out). This left me with only 40 features. Hifens and parenthesis were stripped out from their names.

The last step was to take the average of each measure for each subject and activity. The resulting dataset, containing 42 variables (columns) and 180 observations (rows), is saved in the averages.txt file, which is generated by the analysis script as instructed by ReadMe.

Variable descriptions

All variables here refer to variables found on the averages.txt file, which is actualy comma-separated.

The first two variables define "who did what":

subject - The ID for the tested subject
activity - The name for the considered activity

The other 40 variables are the average, with respect to time, of the measures taken of each individual (subject) for each activity. They are normalized within the [-1, 1] range.

tBodyAccMeanX - Mean of body acceleration, X-axis
tBodyAccMeanY - Mean of body acceleration, Y-axis
tBodyAccMeanZ - Mean of body acceleration, Z-axis
tBodyAccStdX - Standard deviation of body acceleration, X-axis
tBodyAccStdY - Standard deviation of body acceleration, Y-axis
tBodyAccStdZ - Standard deviation of body acceleration, Z-axis
tGravityAccMeanX - Mean of gravity acceleration, X-axis
tGravityAccMeanY - Mean of gravity acceleration, Y-axis
tGravityAccMeanZ - Mean of gravity acceleration, Z-axis
tGravityAccStdX - Standard deviation of gravity acceleration, X-axis
tGravityAccStdY - Standard deviation of gravity acceleration, Y-axis
tGravityAccStdZ - Standard deviation of gravity acceleration, Z-axis
tBodyAccJerkMeanX - Mean of Jerk signals for body acceleration, X-axis
tBodyAccJerkMeanY - Mean of Jerk signals for body acceleration, Y-axis
tBodyAccJerkMeanZ - Mean of Jerk signals for body acceleration, Z-axis
tBodyAccJerkStdX - Standard deviation of Jerk signals for body acceleration, X-axis
tBodyAccJerkStdY - Standard deviation of Jerk signals for body acceleration, Y-axis
tBodyAccJerkStdZ - Standard deviation of Jerk signals for body acceleration, Z-axis
tBodyGyroMeanX - Mean of body angular velocity, X-axis
tBodyGyroMeanY - Mean of body angular velocity, Y-axis
tBodyGyroMeanZ - Mean of body angular velocity, Z-axis
tBodyGyroStdX - Standard deviation of body angular velocity, X-axis
tBodyGyroStdY - Standard deviation of body angular velocity, Y-axis
tBodyGyroStdZ - Standard deviation of body angular velocity, Z-axis
tBodyGyroJerkMeanX - Mean of Jerk signals for body angular velocity, X-axis
tBodyGyroJerkMeanY - Mean of Jerk signals for body angular velocity, Y-axis
tBodyGyroJerkMeanZ - Mean of Jerk signals for body angular velocity, Z-axis
tBodyGyroJerkStdX - Standard deviation of Jerk signals for body angular velocity, X-axis
tBodyGyroJerkStdY - Standard deviation of Jerk signals for body angular velocity, Y-axis
tBodyGyroJerkStdZ - Standard deviation of Jerk signals for body angular velocity, Z-axis
tBodyAccMagMean - Mean of the magnitude of body acceleration
tBodyAccMagStd - Standard deviation of the magnitude of body acceleration
tGravityAccMagMean - Mean of the magnitude of gravity acceleration
tGravityAccMagStd - Standard deviation of the magnitude of gravity acceleration
tBodyAccJerkMagMean - Mean of Jerk signals for the magnitude of body acceleration
tBodyAccJerkMagStd - Standard deviation of Jerk signals for the magnitude of body acceleration
tBodyGyroMagMean - Mean of the magnitude of body angular velocity
tBodyGyroMagStd - Standard deviation of the magnitude of body angular velocity
tBodyGyroJerkMagMean - Mean of Jerk signals for the magnitude of body angular velocity
tBodyGyroJerkMagStd - Standard deviation of Jerk signals for the magnitude of body angular velocity