How to Access List Elements

How to access list elements in R?

There is no row attribute in a list. A list can have a length attribute which is 6 (based on the image). So, if we need to extract the value 654, which is the 2nd element of the vector which is the 2nd element of the list

change_points[[2]][2]

The change_points[[2]] extracts the 2nd list element as a vector and then use [2] to extract the 2nd element of the vector

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When we specify the index as 1, it returns the first element only

sapply(change_points,`[`, 1)

Here, the sapply is looping over all the list elements and extracting the 1st element. If it should be the second element, change the 1 to 2. But, we only need the value of the second list element, so looping over all elements is not needed

How to access list element in FEEL list literal expression in DMN?

In FEEL, the list's elements index starts at 1.

So the expression you want to access first animal object, actually is:

animals[family = "dog" and color = "white"][1]

This is documented in the DMN specification at page 126:

The first element of a list L can be accessed using L[1] and the last
element can be accessed using L[-1].

To provide a more friendly reference, this is also documented in Drools documentation

Elements in a list can be accessed by index, where the first element
is 1. Negative indexes can access elements starting from the end of
the list so that -1 is the last element.

...and equivalently for the productized Red Hat documentation version as well:

How to Access List's elements in c#

You can initialise your list like this:

var list = new List<List<int>>()
{
    new List<int>() {2, 1 },
    new List<int>() {3, 0 },
    new List<int>() {5, 1 }
};

And then you can access each element like this:

var x = list[0][1]; // 1
var y = list[1][0]; // 3

And you can access each inner list like this:

var inner = list[0];// List<int> (2, 1)

And you can update the list like this:

list[0][1] = 42;

or

list[0] = new List<int>() { 10, 11 };

EDIT: How to initialise the list with 10 lists of 1, 1

var list = new List<List<int>>();
for(var i=0;i<10;i++)
{
    list.Add(new List<int>() {1, 1});
};

Accessing Python Lists by index

Note, it may be overkill, but if you are coming from R, you may consider the numpy/pandas libraries for the sort of functionality you would be used to, so, using a numpy.ndarray instead of a list object, you can use:

>>> import numpy as np
>>> arr = np.array(["a", "b", "c", "d", "e", "f", "g"])
>>> arr[np.r_[1, 3:6]]
array(['b', 'd', 'e', 'f'],
      dtype='<U1')

The indexing for numpy/pandas data structures will be more familiar to an R user. Python is not a domain-specific, statistical programming language, it is general purpose, so this sort of fancy-indexing isn't built-in.

Access n:th element of every list in list of lists

when you are enumerating over the list in the for loop:

for word in words:
    pass // do something

You have already accessed the element in the list and stored it in word.

As such, word[0] in your loop would be accessing the first element in your word tuple which is not what you'd like to do.

Instead, you'd like to access word[2] in your tuple, so something like this should work:

first_list = [(0, 'Gallery', 'PROPN', 'nsubj'), (1, 'unveils', 'VERB', 'root'), (2, 'interactive', 'ADJ', 'amod')]

second_list = [(0, 'A', 'DET' 'det'), (1, 'Christmas' , 'PROPN', 'compound'), (2, 'tree' ,'NOUN', 'nsubjpass')]

def print_word_pos(words):
    for word in words:
        print(word[2])

print_word_pos(first_list)
print_word_pos(second_list)

Another thing is that you should not be naming your lists as list since list is a reserved python keyword and might (will) cause conflict later down the line.

Now if the first two lists were combined, you'd want to loop over each list and then for each word in that list, print out the part of speech.

def print_word_pos(list_of_words):
    for words in list_of_words:
        for word in words:
            print(word[2])

Proper way to access list elements in R

All these methods give different outputs

[ ] returns a list

[[ ]] returns the object which is stored in list

If it is a named list, then

List$name or List[["name"]] will return same as List[[ ]]

While List["name"] returns a list, Consider the following example

> List <- list(A = 1,B = 2,C = 3,D = 4)
> List[1]
$A
[1] 1

> class(List[1])
[1] "list"
> List[[1]]
[1] 1
> class(List[[1]])
[1] "numeric"
> List$A
[1] 1
> class(List$A)
[1] "numeric"
> List["A"]
$A
[1] 1

> class(List["A"])
[1] "list"
> List[["A"]]
[1] 1
> class(List[["A"]])
[1] "numeric"

How to access and display specific list item in flask

here is your answer

<li>{{list[2]}}</li>

No need to print the whole list if you don't want to, just pass the index.

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