Reshape 2 Exercises

August 26, 2016
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(This article was first published on R-exercises, and kindly contributed to R-bloggers)

The `Reshape 2` package is based on differentiating between identification variables, and measurement variables. The functions of the `Reshape 2` package then “`melt`” datasets from wide to long format, and “`cast`” datasets from long to wide format.

Required package:
`library(reshape2)`

Answers to the exercises are available here.

Exercise 1

Set a variable called “`moltenMtcars`“, by using the `melt()` function to format “`mtcars`” to long format using the id variables, “`cyl`” and “`gear`“.

Exercise 2

Set a variable, “`CarSurvey`“, using `dcast()` to reformat “`moltenMtcars`” to wide format, with “`cyl`” and “`gear`” in the first two columns. The aggregation function is “`mean`“.

Exercise 3

Using the `melt()` function, format “`airquality`” with 1 measurement per Month/Day date. Set a variable called “`weatherSurvey`“.

Exercise 4

Specify the name of “`weatherSurvey`” column 4 as “`Condition`“, and the name of column 5 as “`Measurement`“, using the `melt()` formula in Exercise 3.

Exercise 5

Use `dcast()` to format “`weatherSurvey`” from long to wide, with `Month` and `Day` as the first 2 columns. Set a new variable, “`airqualityEdit`“.

Exercise 6

`acast()` converts a long-format “`molten`” data frame into a wide-format vector/matrix/array.

Set a new variable, “`AirQualityArray`“, via using `acast()` to re-format, “`weatherSurvey`“, by `Day`, `Month`, and `Condition`.

Exercise 7

Use the `acast()` function to get the means of “`weatherSurvey`” measurement variables by month. Also, remove not available values.

Exercise 8

Use the “`margins =`” parameter of `acast()` in order to include the means of all measurement variables in the formula from Exercise 7.

Exercise 9

Use the `recast()` function to combine the `melt()` operation from Exercise 1, and the `dcast()` operation from Exercise 2.

Exercise 10

Use the `recast()` function to combine the `melt()` operation from Exercise 4, and the `dcast()` operation from Exercise 5. Return the first 5 rows.

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