Code
    weight Time Chick Diet
159     79    6    14    1
126    168   12    11    1
269     40    0    25    2
215     77   12    20    1
252    135   14    23    2
10     171   18     1    1Consider the dataset.
Means of chicks’s weight by diet.
Mean and standard deviations of chicks’s weight by diet.
# A tibble: 4 × 5
  Diet     Mn StDev    q1    q3
  <fct> <dbl> <dbl> <dbl> <dbl>
1 1      103.  56.7  57.8  136.
2 2      123.  71.6  65.5  163 
3 3      143.  86.5  67.5  199.
4 4      135.  68.8  71.2  185.The underlying ideas behind so much of statistics rely on three ideas/functions and one sentence enhancer.
%>% – make code read (almost) like EnglishThe function group_by is incredibly helpful, but not that exciting.
If we group the dataset ChickWeight by Diet, things change only slightly. But what group_by returns is now ready to be passed into summarise.
The function summarise collapses multiple observations down into one number, for instance into a summary statistic. As we saw before, we can summarize multiple variables at once.
What does the following code do?
We can also summarize multiple variables at once – by group or not.
The function mutate allows us to create new variables and add them to the data frame. Recall our summarized data named
We can create a new variable (column)
In case our new variable isn’t automatically printed, remember we can make R print things for us.
mutate works on any data frame. For instance, you might have two variables that are obviously better off as a ratio.
Summary statistics and a lesson about missing values in R.
# A tibble: 8 × 4
  Family         Mn Total    Sm
  <fct>       <dbl> <int> <dbl>
1 Ailuridae    1.5      1   1.5
2 Canidae      4.43    18  79.8
3 Felidae      2.69    19  51.2
4 Hyaenidae    2.4      4   9.6
5 Mustelidae   3.65    30 110. 
6 Procyonidae  3.08     4  12.3
7 Ursidae      2.1      4   8.4
8 Viverridae  NA       32  83.1We removed NAs from mean calculation and made code (almost) read like English
# A tibble: 8 × 4
  Family         Mn Total    Sm
  <fct>       <dbl> <int> <dbl>
1 Ailuridae    1.5      1   1.5
2 Canidae      4.43    18  79.8
3 Felidae      2.69    19  51.2
4 Hyaenidae    2.4      4   9.6
5 Mustelidae   3.65    30 110. 
6 Procyonidae  3.08     4  12.3
7 Ursidae      2.1      4   8.4
8 Viverridae   2.77    32  83.1Maybe relative brain size matters to you, i.e. heaviest brain relative to body weight.
Then throw in some summarise and find which family has greatest mean brain to body weight ratio.