Overview data

str, summary and other functions

str

See data structure. Shows number of rows and columns in a data frame, classes of the columns, first few elements of each column.

str(iris)

'data.frame':   150 obs. of  5 variables:
 $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
 $ Sepal.Width : num  3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
 $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
 $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
 $ Species     : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...

You can add the option “max.level = X” if you know the object is nested (list inside of list inside of list) so that you don’t print too many nested levels.

head or tail

Shows the beginning or the end of an object (you can specify the number of lines printed with n = X)

head(iris, n = 7)

  Sepal.Length Sepal.Width Petal.Length Petal.Width Species
1          5.1         3.5          1.4         0.2  setosa
2          4.9         3.0          1.4         0.2  setosa
3          4.7         3.2          1.3         0.2  setosa
4          4.6         3.1          1.5         0.2  setosa
5          5.0         3.6          1.4         0.2  setosa
6          5.4         3.9          1.7         0.4  setosa
7          4.6         3.4          1.4         0.3  setosa

tail(iris, n = 3)

    Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
148          6.5         3.0          5.2         2.0 virginica
149          6.2         3.4          5.4         2.3 virginica
150          5.9         3.0          5.1         1.8 virginica

summary

Print column-wise info about data frames, shows relevant data from tests, such as aov or t.test.

summary(iris)

  Sepal.Length    Sepal.Width     Petal.Length    Petal.Width   
 Min.   :4.300   Min.   :2.000   Min.   :1.000   Min.   :0.100  
 1st Qu.:5.100   1st Qu.:2.800   1st Qu.:1.600   1st Qu.:0.300  
 Median :5.800   Median :3.000   Median :4.350   Median :1.300  
 Mean   :5.843   Mean   :3.057   Mean   :3.758   Mean   :1.199  
 3rd Qu.:6.400   3rd Qu.:3.300   3rd Qu.:5.100   3rd Qu.:1.800  
 Max.   :7.900   Max.   :4.400   Max.   :6.900   Max.   :2.500  
       Species  
 setosa    :50  
 versicolor:50  
 virginica :50  
                
                
                

Dimensions

• dim(x)
  • Dimensions of a dataset: For a data frame it is c(1, 2), for a vector it is c(1). -length(x)
  • number of elements in a vector, or columns in a data frame or elements in a list
• ncol or nrow
  • number of columns/rows in a data frame
• names
  • Names of columns of a data frame
  • Names of objects in a named list or named vector

dim(iris)

[1] 150   5

length(iris)

[1] 5

length(iris[,1])

[1] 150

ncol(iris)

[1] 5

nrow(iris)

[1] 150

names(iris)

[1] "Sepal.Length" "Sepal.Width"  "Petal.Length" "Petal.Width"  "Species"     

my_numbers = 1:3; names(my_numbers) = c("A", "B", "C")
names(my_numbers)

[1] "A" "B" "C"