Data Wrangling Techniques in R

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Questions and Answers

What is the purpose of the parse_number() function in the provided context?

  • To calculate the mean and standard deviation of the 'Age' column.
  • To handle missing values in the 'Age' column.
  • To create a new column called 'Age' containing numeric values, replacing the old 'Age' column.
  • To convert character values to numeric values within the 'Age' column. (correct)

Why are NA values still present in the table after using parse_number() to convert the 'Age' column to numeric?

  • The 'Age' column still contains missing values (NA). (correct)
  • The `parse_number()` function cannot handle missing values.
  • The `mutate()` function does not handle missing values properly.
  • The `parse_number()` function is not properly integrated with `mutate()`.

How are missing values handled in the calculations of mean() and sd() in the provided context?

  • By automatically excluding missing values.
  • By using the `na.rm = TRUE` argument in the functions. (correct)
  • By ignoring missing values entirely.
  • By replacing missing values with zeros.

What is the primary purpose of the group_by() function, as used in the provided context?

<p>To calculate summary statistics for each gender group separately. (A)</p> Signup and view all the answers

What is the main purpose of the ungroup() function, as used in the provided context?

<p>To remove unnecessary grouping from the data. (D)</p> Signup and view all the answers

How are percentages calculated in the provided context?

<p>By dividing the number of participants in a specific group by the total number of participants and multiplying by 100. (D)</p> Signup and view all the answers

How is the total number of participants accessed when calculating percentages for different gender categories?

<p>By using the <code>n</code> column from the <code>demo_total</code> data object. (B)</p> Signup and view all the answers

What is the purpose of the round() function in the provided context?

<p>To format numeric values with a specific number of decimal places. (C)</p> Signup and view all the answers

What is the format of the data in the table showing data from the first 3 participants?

<p>Wide format (D)</p> Signup and view all the answers

What is the purpose of the select() function in the process of calculating mean scores for QRP items?

<p>To select specific variables (columns) from the data object. (A)</p> Signup and view all the answers

What is the benefit of using the colon operator (:) in the context of selecting QRP items?

<p>It allows selecting all columns within a specified range. (A)</p> Signup and view all the answers

What is the main goal of transforming the data from wide format to long format?

<p>To facilitate calculating mean scores for each participant. (D)</p> Signup and view all the answers

What is the role of the group_by() function in calculating mean scores for each participant, compared to calculating summary statistics by gender?

<p>The <code>group_by()</code> function is used in both cases, but with different columns. (A)</p> Signup and view all the answers

What is the purpose of the summarise() function in the provided context?

<p>To calculate summary statistics for specific columns in grouped data. (D)</p> Signup and view all the answers

What is the main purpose of knitting a R Markdown file?

<p>To combine code, text, and output into a single document. (A)</p> Signup and view all the answers

What function calculates the number of rows in a dataset?

<p>n() (D)</p> Signup and view all the answers

Why did the summarise() function return NA values for mean_age and sd_age?

<p>The <code>Age</code> column contained non-numeric values, such as strings. (A)</p> Signup and view all the answers

Which of the following functions is NOT part of the "Wickham Six"?

<p>sample() (B)</p> Signup and view all the answers

What is the primary reason for converting the Age column to a numeric data type?

<p>To facilitate the calculation of mean and standard deviation. (A)</p> Signup and view all the answers

What function could be used to extract only the numbers from the Age column?

<p>parse_number() (A)</p> Signup and view all the answers

Which of the following is NOT a function mentioned in the content?

<p>sample() (C)</p> Signup and view all the answers

What is the purpose of using the distinct() function on the Age column?

<p>To identify the unique values present in the <code>Age</code> column. (C)</p> Signup and view all the answers

What is the purpose of using the write_csv() function?

<p>To export data objects as csv files (A)</p> Signup and view all the answers

Which function allows you to include or exclude specific columns in a dataframe?

<p>select() (C)</p> Signup and view all the answers

Which of the following functions does NOT alter the original dataframe?

<p>summarise() (C)</p> Signup and view all the answers

What should be added to improve the calculation of mean height in the starwars dataset?

<p>wrap mean() around height directly (D)</p> Signup and view all the answers

What error occurs if the cols argument is missing in the pivot_longer() function?

<p>The function cannot identify which columns to pivot (C)</p> Signup and view all the answers

What argument should be added to mean() to handle missing values in the starwars dataset?

<p>na.rm = TRUE (A)</p> Signup and view all the answers

Which function is used to organize data into groups in R?

<p>group_by() (D)</p> Signup and view all the answers

What method could you use to transpose a dataframe from wide format to long format?

<p>pivot_longer() (B)</p> Signup and view all the answers

When you want to modify the values of an existing column in a dataframe, which function should you use?

<p>mutate() (C)</p> Signup and view all the answers

What would likely happen if the code omits the grouping argument in summarise()?

<p>It returns all data without any aggregation (C)</p> Signup and view all the answers

What prize does adding the parameter argument for certain columns in summarise() achieve?

<p>Generates summary statistics (C)</p> Signup and view all the answers

In the context of R's tidyverse, which function is primarily for sorting rows in a dataframe?

<p>arrange() (C)</p> Signup and view all the answers

Which argument in the mean() function specifically addresses rows with missing data?

<p>na.rm = TRUE (C)</p> Signup and view all the answers

Flashcards

Data Wrangling

The process of cleaning and transforming raw data into a usable format.

Tidyverse

A collection of R packages designed for data science that share an underlying design philosophy.

summarise() function

An R function used to create summary statistics from a dataset.

n() function

A function that counts the number of rows in a dataset, typically used within summarise().

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Mean

The average value of a numeric dataset, calculated by summing the values and dividing by the count.

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Standard Deviation (sd)

A measure that indicates the amount of variation or dispersion in a set of values.

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NA values

Values in a dataset that are undefined or missing, often indicating data issues.

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distinct() function

An R function used to identify unique values in a specified column of a dataset.

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error=TRUE

Used in R to keep errors for reference in code chunks.

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write_csv() function

A function from the readr package to save data as CSV files.

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Pivoting data

Transforming data from wide format to long format or vice versa.

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pivot_longer()

R function to convert wide data to long format.

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mutate() function

Creates new columns or modifies existing ones in a dataframe.

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Handling missing values

Ignoring NA values during calculations.

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Aggregation in R

Combining data values to produce summary results.

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select() function

Reduces columns in a dataframe by choosing certain variables.

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group_by() function

Organizes data into groups based on specified columns.

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arrange() function

Sorts the rows of a dataframe based on column values.

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cols argument

Specifies which columns to use in pivoting functions.

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Binfet et al. (2021)

Study referenced for therapy dog interventions.

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dog_data_raw.csv

Raw data file used in the exercise for analysis.

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parse_number()

A function in tidyverse to convert character numbers to numeric.

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mutate()

A function in R that adds or modifies columns in a dataframe.

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na.rm

An argument in functions to ignore NA (missing) values during calculations.

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summarise()

A function that computes summary statistics for data subsets.

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group_by()

A function that groups data for calculations by specific categories.

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Percentage calculation

Finding the percentage of a subset compared to the total.

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$ operator

A base R operator used to access specific columns in a dataframe.

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round() function

A function to round numerical results to specified decimal places.

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wide format

Data layout where variables are in separate columns for each observation.

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long format

Data layout where multiple observations are stacked in one column.

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knit function

A process to convert .Rmd files into HTML documents in R.

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rename columns

Changing the names of dataframe columns for clarity.

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summary statistics

Quantitative measures that summarize a set of data points.

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demographics analysis

Examining data regarding the characteristics of a population.

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Study Notes

Data Wrangling Techniques in R

  • Data wrangling (or data preprocessing) in R manipulates data to improve its suitability for analysis.
  • This involves transforming data into the desired structure and format, cleaning data, and making important insights and conclusions possible.
  • Tidyverse package functions (e.g., summarise(), group_by(), select(), filter(), mutate(), arrange()) are central to data wrangling.
  • summarise() calculates summary statistics (e.g., mean, standard deviation).
  • group_by() groups data for calculations within subgroups.
  • select() selects desired columns.
  • filter() selects rows based on conditions.
  • mutate() creates new columns.
  • arrange() sorts data.
  • parse_number() converts character columns to numeric, handling values with text appended ('years').

Data Preprocessing for Analysis

  • Convert character data to numeric, especially when calculations involve mean() and sd().
  • Address missing values with na.rm = TRUE to ensure accurate summary statistics with mean() and sd(), where appropriate.
  • Calculate summary statistics by subgroups (e.g., by gender).

Wide to Long Format Conversion

  • Convert wide format data (with variables in separate columns representing different time-points or categories) to long format which is better structured.
  • This allows for easier calculation of mean scores across multiple columns (e.g., QRP items at Time 1). pivot_longer() is used for converting from wide-format to long-format.
  • Use select() with a range (e.g., col = first:last) for efficiently selecting multiple subsequent columns within a dataframe.

Calculating Summary Metrics

  • Calculate summary metrics, like means and standard deviations, for a given numeric column.
  • Calculate percentages by comparing group values to the total group data.
  • Use base R functions (e.g., $) correctly to access specific elements in dataframes.
  • Use the round() function with a specific number to display a specific number of decimal places while formatting results.
  • Create a new data object with calculated statistics for clarity.

Data Object Saving

  • Export processed data to .csv files (e.g., write_csv()) using the readr package to maintain your data between sessions.

Troubleshooting Data Wrangling Errors in R

  • Incorrect column selection in pivot_longer(): Ensure correct variable to pivot by including specific columns.
  • Missing aggregation functions in summarise(). Ensure aggregation method is applied to ensure correct calculated statistic
  • Missing or incorrect argument na.rm = TRUE: Incorporate na.rm = TRUE properly within calculation functions to address missing data points.

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