2017年4月19日足协杯第2轮大连博阳vs丽江飞虎直播
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Results tagged with list-manipulation
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user 10397
百度 但一些守旧派反对这种改革，依然按照旧的历法在这天送新年礼，庆祝新年。
Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.
10
votes
How to count number of observations/rows within each group
Without a Do loop
Tally[First /@ data]
{{AA, 2}, {CC, 5}, {DD, 3}}
or for speed
Tally[data[[All, 1]]]
{{AA, 2}, {CC, 5}, {DD, 3}}
EDIT:
Testing for a bigger set of data:
data2 = Ta …
- 37.6k
1
vote
The minima for a list
If you are looking for a running minima, then the answer already exists here. If you need it by chunks, then
Some data as an example (you use your own)
data = RandomReal[1, 795000];
The function
…
- 37.6k
13
votes
Accepted
Prepending a constant value to sublists of a list
Rewriting other's using operator forms
I like @eldo's solution, but it can be shorter!
Map[Prepend[-1], list, {2}]
Same for @aardvark2012's
Map[Insert[-1, 1], list, {2}]
Solutions of my own
l …
- 37.6k
1
vote
Quick way to form a list
You should avoid uppercase variables and function names, see this answer.
Also, look at the documentation for Thread as an alternative to the other solutions.
list1 = {{2, 10}, {4, 12}, {6, 17}, {8, …
- 37.6k
0
votes
Extracting a 2 x 2 matrix from a 9 x 9 matrix
If you insist in For and something similar to Print then
With[{prnt = WriteString[$Output, ##] &},
For[i = 1, i <= 9, i = i + 8,
For[j = 1, j <= 9, j = j + 8,
prnt[k[[i, j]], " "]
];
prnt[ …
- 37.6k
8
votes
Accepted
Removing last element of each sublist
Most
You are after Most, Mapped over the list. Notice that f/@l is just a short form for Map[f,l].
Most /@ {{1, 4}, {1, 3, 8}, {7, 12}, {2, 4, 9, 12}, {5, 7, 18,
19, 22}, {3, 5}}
(* {{1}, {1, 3} …
- 37.6k
1
vote
Import Log file and transform
SetDirectory@$TemporaryDirectory;
file = Export["test.log", "{\"a\":19,\"c\":12}\n{\"x\":17,\"y\":15}",
"String"];
Flatten[
ReplaceAll[
ImportString[#, "JSON"] & /@ Import[file, "List"]
, R …
- 37.6k
4
votes
How to obtain a subset (of a 2-d set of points with random coordinates) having monotonically...
benchmark = {{4, 4}, {8, 8}, {14, 12}, {16, 16}, {22, 20}, {26,
24}, {32, 32}, {38, 36}, {44, 40}, {46, 44}, {52, 48}, {58,
56}, {62, 60}, {64, 64}, {74, 72}, {82, 80}, {86, 84}, {92,
88}, …
- 37.6k
3
votes
Gathering a List efficiently
I suggest that instead of {L0, L2, L4, L6, L8} you use {lq[0], lq[2], lq[4], lq[6], lq[8]}.
My approcach
lq = GroupBy[
MapIndexed[{##} &, L]
, Q@*First -> Last@*Last
]
But I have to admit that …
- 37.6k
5
votes
Accepted
Merging two lists as a twisted comb
There is a built in function for that Riffle
Riffle[list1, list2]
A more general version of this question is here
Is there a way to riffle more than two lists?
Where the general solutions for …
- 37.6k
2
votes
Accepted
Deleting elements of a list with a condition
From the documentation, DeleteCases[expr,pattern] removes all elements of expr that match pattern. The second argument is a pattern, not a function. Your second argument is a function that working as …
- 37.6k
8
votes
Select sub-sequences in lists?
Other solutions
MapAt[Last, list, {All, 2}]
(* {{a1, c1}, {a2, c2}, {a3, c3}} *)
list /. {x_, {y_, z_}} -> {x, z}
(* {{a1, c1}, {a2, c2}, {a3, c3}} *)
Benchmark
Large data, 10^7 lines.
largeList …
- 37.6k
5
votes
Swapping two points in a list of points
All these will take {0.8,0.4} and transform it into {0.4,0.8}
Reverse[{0.8,0.4}]
(* {0.4,0.8} *)
{0.8,0.4}/.{x_,y_}->{y,x}
(* {0.4,0.8} *)
RotateLeft@{0.8,0.4}
(* {0.4,0.8} *)
RotateRight@{0.8,0.4 …
- 37.6k
7
votes
Creating new lists
Using belisarius/J.M. but with the new operator form of Cases
Cases[{x_, _, _, y_?Positive, _} :> {x, Log10[y]} ] @ data
- 37.6k
5
votes
Deleting specific elements in a list when they come together
A different solution using SubsetQ and Select. I also prefer ti limit the scope of the variable definitions using With or Module.
With[
{
l = {{"x", "b", "c"}, {"y", "a", "d"}, {"x", "b", "y"}, {" …
- 37.6k