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D Kelly O'Day Excel & R Worlds Mod 2 - Excel & R Worlds: 1

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Module 2Moving Between Excel & R Worlds

Do

See & Hear Read

Learning

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Module 2 Moving Between Excel & R WorldsWhat We’ll Cover

• Identify Essential Concepts that Excel Users need to understand to learn R

• Establish correspondence between R and Excel terminology

• Show same calculations and plots in Excel and R– Start with Excel workbook, basic calculations and simple plot– Export the Workbook to CSV file– Reproduce calculations, plots in R


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Excel & R Worlds30 Minute Video – Walks through Excel & R features

Click video image to start video


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Comparison of Excel & R Worlds

Excel RDisplay Look at Data Look at Script


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Display

• Excel World – See data right on screen– Formulas are not visible, need to select cell to see or use Control ~


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Display

• Excel World – See data right on screen– Formulas are not visible, need to select cell to see or use Control ~

• R World – See script on screen, comparable to seeing formula view in Excel– View Data Options:

• Text Editor (Notepad.exe)• Can view my_data data.frame with R functions:

– my_data shows all data– head(my_data,n) shows first n rows – tail(my_data,n) shows last n rows


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User Interface Point & Click Command Line


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User InterfacePoint & Click versus Command Line

• Excel users very familiar & comfortable with point & click

• To make a chart in Excel 2003, we:– Click chart icon– We follow chart wizard

• By answering wizard prompts, we pass chart parameters to the Excel chart engine


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User InterfacePoint & Click versus Command Line

• Excel users very familiar & comfortable with point & click

• To make a chart in Excel 2003, we:– Click chart icon– We follow chart wizard

• By answering wizard prompts, we pass chart parameters to the Excel chart engine

• R’s approach is to have user directly specify chart parameters in function call:

> plot(anom ~ yr, data = my_Data, type = “l”, col = “red”)


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Data Structure WorkbookWorksheet

ColumnCell

Data.frame (List, Matrix, Array)Vector

Vector[I]


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Data Structure

• Everything is by address: row/col or range name

• Range(B2:B22)• Sheet1!range(“B2:B22”)• B6

Excel World R World• Everything is an object with a name • Column of data is called vector with

name (default is V1)• Group of vectors called data frame• data$Glob or data[2]• data$Glob[5] or data[5,2]


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Data Structure

Excel R

Data group Worksheet dataset with* Same # rows

data.frame

Column of data Column BB2:B100

Vector

Data value in range B3 Vector[3]

Dynamic Data Range

Define Name=offset()

Vectors dynamic


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ColumnCell


Vector[I]

Data Types numericcharacterlogical

numericcharacterlogicalfactor


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Data Types

• Excel & R Have 3 similar data types• Numeric (1, 11, 19.2)• Character (“Joe”, “Bill”)• Logical (T,F)

• R has Factor Data Type


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Factors – What Are They? Why Are They important?

• Data sets often contain categorical data that subdivides data

– Gender (Male, Female)

– Language (English, French, Chinese, etc) – Energy Source (fossil, renewable)

Why use factor data type?1. Data integrity – limits data to

specified levels2. Easy to summarize data by factor

levels3. Multivariate plotting – distinguish

by factor

• Character data type does not ensure data integrity (M/F; m/f, male/female)

• R’s factor () function good for categorical data

>gender_f <- factor(gender, levels = c(“M”, “F”)– Establishes factor gender_f– Sets acceptable values with levels argument

to M or F


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ColumnCell


Vector[I]



Data Summary & Query by Criteria

sumif(); sumproduct();{Array formulas}; Pivot Table

Index (,,,Match(,,),)

as.factor()subset(), tapply()

which()


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How to Summarize Data by Factor

Menu

Array formulas are not user friendly

Excel World R World


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ColumnCell


Vector[I]



Data Summary & Query by Criteria


=Index(,, Match,,),)

as.factor()subset(), tapply()

which()

Missing Values Inconsistent Handling Proper Handling


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Missing Data

• Excel has serious shortcomings when it comes to handling missing data– Blanks can be converted to zero when blank cell is referenced in

formula– Functions like regression can not handle blank cells in range

• R addresses missing data directly– User specifies code for missing data in read.table()– User specifies how to handle missing data in calculations

Video on next slide shows how Excel & R handle missing data


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Missing Data

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ColumnCell


Vector[I]



Data Summary by Criteria


subset()

Missing Values Inconsistent Handling Proper Handling

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