Data Science: Advanced-R Boot CampData Reshaping and Subsetting

Chuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhDChuck Cartledge, PhD

23 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 202023 February 2020

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Table of contents (1 of 1)

1 Intro.

2 Simple ways

3 Data frame reshaping

4 Hands-onLooking at “old” data

5 Q & A

6 Conclusion7 References8 Files

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What are we going to cover?

We’re going to talk about moulding thedata we have into data we want.

Look at lots of different ways tomodify data

Look at lots of different ways toextract data

look at lots of different ways toreshape data

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Atomic vectors, and lists

Subscripts: positive,negative, ordered, duplicate,logical, named

x

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Data frames behave differently

1 When subsetting with asingle index, they behavelike lists and index thecolumns, so df[1:2] selectsthe first two columns.

2 When subsetting with twoindices, they behave likematrices, so df[1:3, ] selectsthe first three rows (and allthe columns).

rm(list=ls())

df

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Make things go away, or not

Assigning the reserved valueNULL to anelement/dimension willremove thatelement/dimension

To assign the reserved valueNULL to anelement/dimension, encloseit in a list()

x

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A lookup table based on abbreviations

Use a look-up table to translatefrom abbreviation to full text.The look-up table has namedentries that correspond exactlywith the items to be “looked-up.”The entire column is returned foreach matched entry.

rm(list=ls())

x

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cbind() and rbind()

The simplest case is when wehave two datasets with eitheridentical columns (both thenumber of and names) or thesame number of rows. In thiscase, either rbind or cbind workgreat.

sport

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Different types of data set joins

Generally there are sevendifferent types:

1 Inner: elements common toboth sets

2 Left outer: elements not inright

3 Right outer: elements not inleft

4 Full outer: all elements in rightand left, but no commonelements

5 Right anti: elements in rightouter and not left inner

6 Left anti: elements in left outerand not right inner

7 Anti inner: elements in leftouter and right outer and notinner

Image from [1].

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Same image.

Image from [1].c©Old Dominion University

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Translate SQL joins into R

Generally there are seven different types:

1 Inner

2 Left outer

3 Right outer

4 Full outer

5 Right anti

6 Left anti

7 Anti inner

See code in attached

"snippet" file.

Ideas from [2].

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Extracting data from data frame

Lots of different ways:

Direct selection based on logicals

base::subset(x, subset, select,drop = FALSE, . . . ) uses logicalto select rows

base::transform( data, . . . )creates or modifies new columns

plyr::arrange(df, . . . ) combinessubset() and transform()

reshape2::melt(data, . . . ) genericfunction that calls specifics basedon data type

reshape2::dcast(data, formula,func, . . . ) cast “melted” datainto a data frame

ChickWeight[(ChickWeight$Diet==4)&

(ChickWeight$Time==21),]

subset(ChickWeight, Diet==4 &

Time == 21)

subset(airquality, Temp > 80,

select = c(Ozone, Temp))

with(airquality, subset(Ozone,

Temp > 80))

transform(airquality,

new = -Ozone,

Temp = (Temp-32)/1.8)

arrange(mtcars, cyl, disp)

arrange(mtcars, cyl, desc(disp))

See embedded file.

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Looking at “old” data

With the Motor Trend cars dataset:

Write a script that:

Converts the mtcars dataset wt column into pounds

Identifies the most fuel efficient vehicle by transmission typeand number of carburetors

Creates a data frame with all the column data for the vehiclesidentified in the previous requirement

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Q & A time.

Q: What was the greatestachievement in taxidermy?A: The Royal Canadian MountedPolice.

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What have we covered?

Looked at different ways to createdata frame, from raw data or otherdata framesLooked at different functions thatdo the same things

Next: String manipulations

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References (1 of 1)

[1] deadman87, Sql joins explained (x-post r/sql),https://www.reddit.com/r/programming/comments/

1xlqeu/sql_joins_explained_xpost_rsql/, 2014.

[2] Dan Goldstein, How to join (merge) data frames (inner, outer,left, right),https://stackoverflow.com/questions/1299871/how-

to-join-merge-data-frames-inner-outer-left-right,2009.

c©Old Dominion University

https://www.reddit.com/r/programming/comments/1xlqeu/sql_joins_explained_xpost_rsql/https://www.reddit.com/r/programming/comments/1xlqeu/sql_joins_explained_xpost_rsql/https://stackoverflow.com/questions/1299871/how-to-join-merge-data-frames-inner-outer-left-righthttps://stackoverflow.com/questions/1299871/how-to-join-merge-data-frames-inner-outer-left-right

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Files of interest

1 Code snippets

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## First codesrm(list=ls())

x