8 List and list indexing

• List in R and Python can include different data types
• List operation differs between two languages

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8.1 R

Lst <- list(x = 5, y = 3.5, w = 'David', z = TRUE, s = 'Another string', v = c(1,3,5))

Index	Explanation	Example.
$	Get the elements by names	Lst$x
[i]	Get the element at the specific location. The outcome is a LIST.	Lst[1]; Lst[3]
[[i]]	Get the element at the specific location. The outcome is the corresponding CLASS.	Lst[[1]]; Lst[[3]]
Positive integer	Get the element at the specific location	Lst[2]; Lst[[2]]
Negative integer	Remove the element at the specific location and return the rest.	Lst[-2]
Zero	Get no element. Only valid with [i].	Lst[0]
Blank	Get all elements. Only valid with [i].	Lst[]
Logical values	Get the element for the location is TRUE. Only valid with [i].	Lst[c(T,T,F,F)]
Names	Get the named element	Lst$x

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8.2 Python

Lst = [5, 3.5, 'David', True, 'Another string', v = c[1,3,5] ]

Python slicing and dicing operations are carried through the following logic: Lst[start:stop:step]

Index	Explanation	Example.
start	The starting position (0 indexing applies)	Lst[2]; Lst[1:]
end	The starting position (0 indexing applies)	Lst[:4]; Lst[1:5]
step	The step values	Lst[1:4:2]; Lst[::-1]
negative integer	Different behaviours depending on start, stop or step

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Important list methods:

append, extend, insert, remove, pop, index, count, sort, reverse

8.3 Python-specific objects

Tuple

• Tuple stores multiple fixed values in a sequence.

• It uses \(()\) to include the values

tup = ("apple", "banana", "cherry", "apple", "cherry", "cherry")

print(tup)

(‘apple’, ‘banana’, ‘cherry’, ‘apple’, ‘cherry’, ‘cherry’)

Set

• Set stores multiple unique values in an unordered collection.

• It uses \({}\) to include the unique values

fset = {"apple", "banana", "cherry", "apple", "cherry", "cherry"}

print(fset)

{‘cherry’, ‘banana’, ‘apple’}

Dictionary

Dictionary stores multiple unordered key:value pairs.

fdict = {"apple": 2, "banana": 1, "cherry": 3}

print(fdict)

{‘apple’: 2, ‘banana’: 1, ‘cherry’: 3}