GettingandCleaningDataProject

Created: 2014-05-19 18:45
Updated: 2014-05-21 16:24
r

README.md

##How to get a Clean Dataset from HAR raw data

###Please read this document carefully before performing the analysis using the provided R script ###By Michael Chen, email: mikcolchen@hotmail.com

The purpose of this R script(run_analysis.R) is to perform the task of collect, work with, and clean the data set as provided by this project. The goal of it is to prepare tidy data that can be used for later analysis. The source of the data is from a research website of UCI shown as below, the second link indicates the location of the source data.

Research Website: http://archive.ics.uci.edu/ml/datasets/Human+Activity+Recognition+Using+Smartphones Data Source: https://d396qusza40orc.cloudfront.net/getdata%2Fprojectfiles%2FUCI%20HAR%20Dataset.zip

From the research website, you may have a quick study on how the Human Activity Recognition research data files were collected. While these data files are raw, to perform data analysis and extract valuable information, the first step is to make the datasets clean and tidy, the rest of this document will explain how this task will be performed using the attached R script "run_analysis.R".

  • Download the zip file from the data source link:

  • Collect, combine and clean the data:

    • Function: RunAnalysis(dataFolder = "./UCI HAR Dataset")

      • dataFolder: Indicates the path and folder in which all the data files are saved. Has default value;

      • Explain: This function will automatically perform the following steps sequentially, and eventually generate a tidy dataset of average values for each measured feature by each activity and each subject:

        1.Merges the training and the test sets to create one data set.

        • Function: CombTrainTest(trainFold, testFold)

          • trainFold: The folder and its path which contains all training data files;
          • testFold: The folder and its path which contains all test data files;
          • Explain: This function will in the first place sequentially combine y_train data, subject_train data and X_train data by columns as training data set, combine y_test data, subject_test data and X_test data by columns as test data set. Then combine training data and test data by rows as a complete data set;

        2.Extracts only the measurements on the mean and standard deviation for each measurement.

        • Function: ExMeanStd(dataSet, featureFile)

          • dataSet: The complete combined data set, generated from step 1;
          • featureFile: The path of the file which contains complete list of measured features as named as features.txt originally;
          • Explain: To filter out the mean and standard deviation measurements together with activity label and subject, the function scans the vector of feature meansurements (features.txt), find out the indices of the elements of which the values contain either "mean" or "std", then by using those indices it can figure out the indices of the columns which represent the mean and STD measuments of the complete data set, subsequently, a subset of the complete combined data set which only contains mean and STD measurements can be extracted. In the end, this function calls function AddColNames, passes the extrated mean/STD sub data set and a vector of mean/STD feature measurement names as parameters to it which is responsible to add descriptive variable names to the mean/STD sub data set, function AddColNames will be introduced under point number 4;

        3.Uses descriptive activity names to name the activities in the data set.

        • Function: NameActi(dataSet, labelFile)

          - dataSet:   The extracted data set which only contains activity lable, subject and mean or STD measured features, generated from step 2;
          
          • labelFile: The path of activity definition file as named as activity_labels.txt originally;
          • Explain: Function reads activity_labels.txt to a data set, then merges the mean/STD data set with this activity definition data set by the key column "label", afterward it moves the activity names column to the first column position and in the mean time drop column lable, as a result the label column was replaced by descriptive activity names column. The result of this function will give out a data set of 10299 observations and 81 variables, it is a tidy data set because it meets all the three principles as a tidy data set;

        4.Appropriately labels the data set with descriptive variable names.

        • Function: AddColNames(dataSet, vNameSet)

          • dataSet: The extracted data set which only contains activity lable, subject and mean or STD measured features;
          • vNameSet: A character vector of which the elements will be used to name the feature measurements variables in the data set;
          • Explain: The value of parameter vNameSet will be passed from function ExMeanStd since it is called within function ExMeanStd. As qualified descriptive variable names, first of all, the variable name must be able to convey the meaning of the specific variable; Secondly, the letters are all in lower case; Thirdly, the names don't contain any symbols other than "." which is used to separate the words if the name is consisted of several words. Therefore, the value of parameter vNameSet must be formatted accordingly since it is just a part of the list of feature measurements (from features.txt, please refer to the explanation in function ExMeanStd), as a result of the format, symbol "-" or "()" in the name of each feature measurement were replaced with symbol ".", and all characters are in lower case, then at this point each feature measurement variable in the data set could be re-named after each element of the formatted name vector sequentially;

        5.Create new tidy data set with the average of each variable for each activity and each subject.

        • Function: GetAvgSet <- function(dataSet, expDest = "./UCI HAR Dataset/AvgTidySet.txt")

          • dataSet: Data set generated by step 3;
          • expDest: Indicate where you want to save the exported data set file, has default value;
          • Explain: By using group calculatin function ddply, calculates the mean value of the observations of each feature measurement column for each activity and each subject, then for the new data set, re-name each feature measurement variable by adding "avg." in front of their original names, it is a tidy data set because it meets all the three principles as a tidy data set.

NOTE: FOR A REFERENCE OF THE ACTUAL MEANING OF EACH COLUMN OF THE FINAL TIDY DATASET PLEASE READ THE CODE BOOK!

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