Cereal data example

The purpose of this document is to introduce some very basic aspects of using R Markdown.

Basics

A few years ago, I collected information on the nutritional content of dry cereals at a grocery store. This was done by first noting that one side of one aisle in many grocery stores usually contains all the cereals within a store. For example, below shows what the cereal aisle used to look like in the HyVee at 5020 N 27th St. before its recent renovation:

My research hypothesis was that there were different mean nutritional contents by shelf. For example, lower shelves may have more sugar content cereals than higher shelves.

The data used for this example was collected from a store a few years ago (not the HyVee in the picture). Note that there were only four shelves at this store and my sample size was 10 from each shelf. Below is how I read the data into R.

cereal <- read.csv(file = "C:\\data\\cereal.csv")
head(cereal)

##   ID Shelf                               Cereal size_g sugar_g fat_g
## 1  1     1 Kellog's Razzle Dazzle Rice Crispies     28      10     0
## 2  2     1            Post Toasties Corn Flakes     28       2     0
## 3  3     1                Kellogg's Corn Flakes     28       2     0
## 4  4     1               Food Club Toasted Oats     32       2     2
## 5  5     1                     Frosted Cheerios     30      13     1
## 6  6     1             Food Club Frosted Flakes     31      11     0
##   sodium_mg
## 1       170
## 2       270
## 3       300
## 4       280
## 5       210
## 6       180

The shelves are numbered from lowest (1) to highest (4).

We need to adjust the nutritional content variables (sugar_g, fat_g, and sodium_g) for the serving size because cereal boxes tend to have different serving sizes. Below is how I make the adjustment in R.

cereal$sugar <- cereal$sugar_g/cereal$size_g
cereal$fat <- cereal$fat_g/cereal$size_g
cereal$sodium <- cereal$sodium_mg/cereal$size_g
head(cereal)

##   ID Shelf                               Cereal size_g sugar_g fat_g
## 1  1     1 Kellog's Razzle Dazzle Rice Crispies     28      10     0
## 2  2     1            Post Toasties Corn Flakes     28       2     0
## 3  3     1                Kellogg's Corn Flakes     28       2     0
## 4  4     1               Food Club Toasted Oats     32       2     2
## 5  5     1                     Frosted Cheerios     30      13     1
## 6  6     1             Food Club Frosted Flakes     31      11     0
##   sodium_mg      sugar        fat    sodium
## 1       170 0.35714286 0.00000000  6.071429
## 2       270 0.07142857 0.00000000  9.642857
## 3       300 0.07142857 0.00000000 10.714286
## 4       280 0.06250000 0.06250000  8.750000
## 5       210 0.43333333 0.03333333  7.000000
## 6       180 0.35483871 0.00000000  5.806452

For example, the sugar value for Kellogg’s Razzle Dazzle Rice Crispies is \(\textrm{(sugar grams per serving)/(# of grams per serving size)}\) = 10/28 = 0.3571.

Alternatively, taking advantage of knitr, the calculation can be automatically done here using R: \[\textrm{(sugar grams per serving)/(# of grams per serving size)} = 10 / 28 = 0.3571429.\]