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Getting and Cleaning Data - Coursera Course. Course Project

Paul Johnston 12/8/2014

Codebook.md

This is the codebook for this project. See the README.txt file for details on the process for performing the analysis.

Data for the project is located here. https://d396qusza40orc.cloudfront.net/getdata%2Fprojectfiles%2FUCI%20HAR%20Dataset.zip

See the included README.txt file in that zip for details on the variables in the source data and a description of each.

activityData

Here is a description of the set generated in a variablke called "activityData" in the environment as a result of executing the analytics using the run_analysis.R script

> activityData
Source: local data frame [10,299 x 81]

   activity_name subject_id tbodyacc_mean_x tbodyacc_mean_y tbodyacc_mean_z tbodyacc_std_x tbodyacc_std_y tbodyacc_std_z tgravityacc_mean_x
1       STANDING          2       0.2571778     -0.02328523     -0.01465376     -0.9384040     -0.9200908     -0.6676833          0.9364893
2       STANDING          2       0.2860267     -0.01316336     -0.11908252     -0.9754147     -0.9674579     -0.9449582          0.9274036
3       STANDING          2       0.2754848     -0.02605042     -0.11815167     -0.9938190     -0.9699255     -0.9627480          0.9299150
4       STANDING          2       0.2702982     -0.03261387     -0.11752018     -0.9947428     -0.9732676     -0.9670907          0.9288814
5       STANDING          2       0.2748330     -0.02784779     -0.12952716     -0.9938525     -0.9674455     -0.9782950          0.9265997
6       STANDING          2       0.2792199     -0.01862040     -0.11390197     -0.9944552     -0.9704169     -0.9653163          0.9256632
7       STANDING          2       0.2797459     -0.01827103     -0.10399988     -0.9958192     -0.9763536     -0.9777247          0.9261366
8       STANDING          2       0.2746005     -0.02503513     -0.11683085     -0.9955944     -0.9820689     -0.9852624          0.9265862
9       STANDING          2       0.2725287     -0.02095401     -0.11447249     -0.9967841     -0.9759063     -0.9865970          0.9255553
10      STANDING          2       0.2757457     -0.01037199     -0.09977589     -0.9983731     -0.9869329     -0.9910219          0.9241734
..           ...        ...             ...             ...             ...            ...            ...            ...                ...

This contains merged training and test sets to create one data set, but only measurements for variables representing the standard deviation (acitivyt name contains std) and mean (acitivty name contains mean) have been extracted from the source data set. There is one row per activity per subject for all variables measured each time they were measure for each subject and acitivy.

  • activity_name: values in this field are taken from the source "activity_labels.txt" file and represent the activity
  • subject_id: this is a unique value representing the subject who carried out the experiment
  • The other columns all represent a measure of variables on features in the source signal data set.

tidyActivityData

This data is then further analyed to create a "tidy.txt" data set with exactly 4 columns:

  • activity_name: values in this field are taken from the source "activity_labels.txt" file and represent the activity
  • subject_id: this is a unique value representing the subject who carried out the experiment
  • measure: this contains the name of the measured variable
  • mean_value: this contains the mean value of the mesaured variable across all measurements of that variable for a particular activity and subject.

This is exactly one row per activity per subject per measure in this tidy data set. Data is sorted by activity_name then subject_id then measure. Post analysis, this tidy data has also been made available in an environment value called "tidyActivityData":

> tidyActivityData
Source: local data frame [14,220 x 4]
Groups: activity_name, subject_id

   activity_name subject_id            measure  mean_value
1         LAYING          1    tbodyacc_mean_x  0.22159824
2         LAYING          1    tbodyacc_mean_y -0.04051395
3         LAYING          1    tbodyacc_mean_z -0.11320355
4         LAYING          1     tbodyacc_std_x -0.92805647
5         LAYING          1     tbodyacc_std_y -0.83682741
6         LAYING          1     tbodyacc_std_z -0.82606140
7         LAYING          1 tgravityacc_mean_x -0.24888180
8         LAYING          1 tgravityacc_mean_y  0.70554977
9         LAYING          1 tgravityacc_mean_z  0.44581772
10        LAYING          1  tgravityacc_std_x -0.89683002
..           ...        ...                ...         ...