Questions tagged [list]

is for the list object in Lisp programming. A list represents a sequence of zero or more elements. Emacs Lisp relies extensively on the list data structure; it is a fundamental building block. Emacs provides many facilities for building, modifying, extending, and efficiently handling list data structures.

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1answer
33 views

Print matching strings line by line

I was trying to use this code shared by @JordonBiondo over here to collect regex matches in a list. (defun matches-in-buffer (regexp &optional buffer) "return a list of matches of REGEXP in ...
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0answers
39 views

Emacs freezes when using split-string in recursive function

I'm trying to figure out why my emacs keeps freezing when running this set of functions to split a string into a list of pairs. Is there some significant overhead happening when using string-split? Is ...
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2answers
66 views

Get first n elements of a list

How can I get the first N elements of a list? I know I can use subseq: (subseq '("one" "two" "three" "four" "five") 0 2) Yet when I use subseq, it produces one of the following results: on the ...
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1answer
42 views

Would (cycle-list <ls>) be a bad idea?

Would you consider something like this a bad practice? (defun cycle-list (ls &optional backward?) "Given any list, returns the next element each time it is called." (let* ((last-pos (- (...
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1answer
186 views

Circular list use of “#”

Looking at this, I see (setq x '#1=(a #1#)) but this evaluates to (a #0). As I understand, this should be (a #1=(a #1#)). But then what syntax makes #0 mean #1=(a #1#)? In general what is # doing in ...
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1answer
35 views

Make forward-list search for specific symbol only

Is there a way to make forward-list and backward-listsearch for specific symbols (such as 「」『』) only? I have code that make use of these functions to iterate through 「」『』 pairs in plain text. But ...
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2answers
178 views

How to subtract 1 from the nth element of a list of numbers?

How do I subtract 1 from the second element of the list (3 6)? (setq x '(3 6)) (- (nth 1 x) 1) The above quote does the math but does not return a modified list.
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2answers
47 views

Add a number to every item in list

How do I add a number, say 2, to every item in a list? (setq x '(1 2)) (+ 2 x) (mapcar '2+ x) (loop for i in x do (+ 2 i)) (dolist (i x) (+ 2 i)) None of the above work.
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3answers
318 views

Move point inwards while counting number of nested parentheses without throwing an error

I would like to write a function that counts the number of nested parentheses while moving the cursor to the innermost bracket without throwing an error. (defun count-and-move () (interactive) ...
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4answers
240 views

Remove multiple elements from a list

Given '(a b c d), how would I remove b and c to end up with '(a d)? Is there a "right" way to remove multiple, distinct elements from a list? Obviously, one could do (delete 'c (delete 'b '(a b c d))...
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2answers
163 views

Apply different function to each element in list?

I have a time-stamp of a video formatted as "00:00:00,000" such that "%H:%M:%s,%3N". I am want to eventually use this timestamp as part of an in-interval-p function where I take two timestamps and a ...
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2answers
33 views

How to check if a list ends with another list?

Currently I'm using a fairly inefficient way to check if one list uses another list at it's end. Is there a more efficient way to do this? (defun is-in-list (ls-haystack ls-ends-with) (catch 'found ...
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2answers
99 views

How to check if two lists share any elements?

Besides looping over list items and comparing, what is a good way in elisp to check if there are any shared items between two lists? For example, in Python this can be done with sets or list ...
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1answer
43 views

Is function `list` equivalent to using `cons` with a final cdr of `nil`?

I'm trying to explain Elisp to 5th and 6th graders and I tell them that (+ 1 2) evaluates to 3 and not (3). So if I do want something that evaluates to (3) would I just evaluate ((+ 1 2))? No! This ...
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1answer
241 views

Melpa - 'Failed to download melpa'

I am on a fresh install of emacs 26.3, and I have the following in my init.el: (require 'package) (add-to-list 'package-archives '("melpa", "https://melpa.org/packages") t) (package-...
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2answers
40 views

Representing leading zeroes in a list

I would like to have this table #+NAME: addition-table | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | |---+----+----+----+----+----+----+----+----+----+----| | 0 | 00 | 01 | 02 | 03 | 04 | ...
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1answer
715 views

Are the graphical depictions in docs drawed in manual labour?

There are tons of pretty graphical depictions in the emacs(or elisp) docs such as x1: -------------- -------------- -------------- | car | cdr | | car | cdr | | car | ...
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1answer
46 views

Map each element of a list over every element of another list

Let's assume I've got two lists: ("A" "B" "C" "D") and ("+" "-"). I want to concatenate each element of the first list with every element of the second to get ("A+" "A-" "B+" "B-" ... ). Is there a ...
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1answer
30 views

Inline elements of variable list value in rx() macro call [duplicate]

Is there a more compact way to make use of the rx macro in cases where we want to inline a list of strings from a variable? Such as (defconst c++20-new-keywords-list (list "char8_t" "import" ...
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1answer
102 views

Elisp: How to accumulate function return into a list

I have this small snippet of Elisp code that decodes kernel traces: (defvar projbase "/my/proj/base") (setq my_shell_output (substring (shell-command-to-string (concat "/home/demetra/scripts/...
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2answers
83 views

Orgmode automatically increment an unordered list

I use org-mode for planning projects and tasks, etc. Say I am reading a book and I want to track my progress chapter by chapter. I want to create a list of repetitive elements with an incremented ...
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1answer
56 views

trying to make a self-modifying function [duplicate]

I'm trying to make a function that returns a list of perfect numbers: A perfect number is a positive integer that is equal to the sum of its proper positive divisors For instance, 28 is perfect ...
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1answer
183 views

Removing the last element of a list

Is there a simpler way to remove the last element of a list than this? (setq list (reverse (cdr (reverse list))))
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1answer
164 views

Shortening trees list with (setcdr (nthcdr 2 trees) nil)

I am starting to learn elisp and working through this tutorial https://www.gnu.org/software/emacs/manual/html_node/eintr/kill_002dnew-function.html and I do not understand this basic example: (setq ...
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1answer
45 views

midnight-mode add-to-list Format specifier doesn't match argument type

I've been trying to get midnight-mode to add to the following list. I have a feeling it has to do with an elisp error in my config I'm not seeing. It works fine with setq, but with add-to-list I get a ...
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1answer
165 views

How to write a list literal with conditional items? [duplicate]

Given a list literal '(1 2 3) is it possible to conditionally include parts of the list? eg: '(1 2 3 (when thing-is-true '(10 11 12))) 4 5 6) Which would result in '(1 2 3 4 5 6) or '(1 2 3 ...
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1answer
276 views

Org Mode. Set separation length between elements of a list

I have noticed there is a big gap between the elements of a list when exporting to PDF. Is there a way to modify it?
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1answer
53 views

List variable that is set to one list or another depending on condition

I am trying to create a list variable that can be set to one list or another depending on a condition. What I have so far is as follows. (let ((l (if local list1 list2))) ; Append items to the list ...
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1answer
46 views

How can i add same value to every item in list, turning it into alist?

I tried to use this code, but it returns (k k k k k) (mapcar (lambda (x) 'cons x '(k)) '(a b c d e)) What am i doing wrong here? Why doesn't cons work?
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4answers
421 views

Map function onto nested list?

Q: how can I map a function onto elements of nested lists? For flat lists, we can use mapcar to apply a function to each element of the list: (setq flat '("kittens" "puppies" "otters" "bunnies")) (...
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0answers
398 views

When to use quote for lists? Modifying quoted lists in Elisp

The Common Lisp Hyper Spec says: The consequences are undefined if literal objects (including quoted objects) are destructively modified. This is further motivated at the Constant Modification ...
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2answers
150 views

Evaluating symbol in function arguments affected by destructive operations?

While evaluating a function call, the arguments is from left to right. For example, (let ((x '(1 2 3))) (list (nreverse x) x)) ;; => ((3 2 1) (1)) The first argument (nreverse x) evaluates to (...
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2answers
107 views

Does `car` on an non-lazy function generated list evals the whole list?

I want to get in a huge directory the first file which satisfies some condition, something like (require 'seq) (require 'f) (defun lazy-filter-file (pred path) (car (seq-filter pred (f--files path ...
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2answers
280 views

How to delete all list elements matching a regexp?

Given a list: (setq mylist '("a1" "a2" "b1" "b2")) How to delete all elements that match ^a? What I want is "a1" and "a2" deleted, only left "b1" and "b2" in the list.
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2answers
59 views

Arbitrary length lists as argument for interactive function

Say I have a defun with a dolist inside that I want to be able to pass a string that is then converted to a list with a length equal to the number of words in said string via the minibuffer, so ...
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1answer
29 views

Comparing `system-configuration-options` to a user-specified list

In this example, the system-configuration-options is a string: "--prefix=/Users/HOME/.0.data/.0.emacs/.0.x11 --with-x --with-ns=no --enable-checking=yes,glyphs --enable-check-lisp-object-type --...
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0answers
102 views

Directed Acyclic Graphs in Emacs Lisp

Emacs Lisp has support for lists (naturally), association lists, and property lists, vectors, and hash tables. Does it have support for directed acyclic graphs (DAGs)? I have not found a DAG API in ...
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1answer
101 views

Updating `dired-directory` after renaming a file

Q:   I have a list of strings: '("apple" "pear" "peach" "nectarine" "watermelon"). How can I replace "peach" with "plum" and maintain the same order of fruits?  [CAVEAT: The list may be very long ...
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1answer
145 views

Replacing autoref command format specification in auctex's font-latex-match-reference-keywords-local

With some help I have redefined the autoref command to take an optional argument, see https://tex.stackexchange.com/questions/428229/autoref-with-optional-argument-text-in-generated-link Now I am ...
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4answers
316 views

How to mapcar uneven lists?

I am aware I can use mapcar to join 2 lists into pairs, however all the map functions seem to quit at the shortest list. This for example (cl-mapcar #'concat '("1" "2" "3" "4") '("a" "b" "c")) ...
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2answers
326 views

Sort list by decreasing length of the strings

I have this list: (setq MYLIST '("J. Phys." "New. J. Phys." "J. Phys. Soc. Jap." "Phys. Plasmas")) How can I get a new list ordered by the decreasing ...
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2answers
721 views

Adding many items to a list

What is the proper way to add many items to a list? I assume just using many add-to-lists is not the normal way?
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1answer
40 views

cons a symbol with a variable and return as a symbol [duplicate]

How can I make fun2 return as the same as fun1? (defun fun1 () '((hello . "test"))) ; <= returns ((hello . "test")) (defun fun2 (str) '((hello . str))) ; <= this is wrong! should return ((...
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2answers
53 views

How to define a bundle of variable-and-function pairs?

I want to define a bundle of variable-and-function pairs, e.g.: vl/path-doc points to my often used path, and vl/open-path-doc is used for open it in dired-mode. I tried this piece of code: (setq ...
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2answers
424 views

How do I rotate list elements?

Q: how do I rotate the elements of a list such that last becomes first? Given a list of arbitrary length, how do I rotate the list non-destructively such that the last element becomes the first ...
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1answer
221 views

How to pop an arbitrary element from a list?

Q: how do I pop an arbitrary element from a list? Given the list '(a b c d e), pop returns a and destructively modifies the list to '(b c d e). How can I generalize this function so I could pop an ...
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1answer
60 views

Doubly-linked list package

Are there any good packages for Emacs that implement doubly-linked lists? I know I could make them myself, but I'd rather not re-invent the wheel.
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3answers
94 views

How can I convert a list of integers to a string?

Let's say I have a list of integers, representing year, month, day for a date: (2017 8 21) and I want to format the list in one function call, as in (format "%04d-%02d-%02d" 2017 8 21) Is there an ...
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1answer
490 views

How to sort an association list (alist)?

Is there a way to sort an association list? In my case I would like to sort the alist elements by the values in each list element (represented by the integers in the example below). Example: (setq ...
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1answer
48 views

How to create and traverse a multidimensional list

I have code like this: (let* ((l1 '(1 2 3)) (l2 '(4 5 6)) (l3 '(7 8 9)) (ml '(l1 l2 l3))) (dolist (l ml) (message "%s" l) (dolist (e l) (message "%s" e)))) But ...