Mapping a function f[xi_,xj_] over a list {x1, …, xn} with the i < j restriction
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I am often facing the situation where I have a list ${...x_k...}$ and where I want to compute:
$$
{...f[x_i,x_j]...}text{ with } i<j
$$
Unfortunately, I have not been able to find an elegant solution for this problem. What I'm doing right now seems horrible to me (indirections etc...):
n = 4;
x = Table[RandomReal, n]
{0.547984, 0.601967, 0.000917483, 0.738287}
Map[f[Apply[Sequence, x[[#]]]] &,
Flatten[Table[{i, j}, {i, 1, n}, {j, i + 1, n}], 1]]
{f[0.547984, 0.601967], f[0.547984, 0.000917483], f[0.547984,
0.738287], f[0.601967, 0.000917483], f[0.601967, 0.738287], f[0.000917483, 0.738287]}
(in real situation f is defined f[xi_,xj_]:= xi-xj for instance)
Question: what is a better (builtin?) solution?
list-manipulation programming
asked May 28 at 11:14
Picaud VincentPicaud Vincent
1,5827 silver badges18 bronze badges
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$begingroup$
I am often facing the situation where I have a list ${...x_k...}$ and where I want to compute:
$$
{...f[x_i,x_j]...}text{ with } i<j
$$
Unfortunately, I have not been able to find an elegant solution for this problem. What I'm doing right now seems horrible to me (indirections etc...):
n = 4;
x = Table[RandomReal, n]
{0.547984, 0.601967, 0.000917483, 0.738287}
Map[f[Apply[Sequence, x[[#]]]] &,
Flatten[Table[{i, j}, {i, 1, n}, {j, i + 1, n}], 1]]
{f[0.547984, 0.601967], f[0.547984, 0.000917483], f[0.547984,
0.738287], f[0.601967, 0.000917483], f[0.601967, 0.738287], f[0.000917483, 0.738287]}
(in real situation f is defined f[xi_,xj_]:= xi-xj for instance)
Question: what is a better (builtin?) solution?
list-manipulation programming
asked May 28 at 11:14
Picaud VincentPicaud Vincent
1,5827 silver badges18 bronze badges
$endgroup$
add a comment
|
$begingroup$
I am often facing the situation where I have a list ${...x_k...}$ and where I want to compute:
$$
{...f[x_i,x_j]...}text{ with } i<j
$$
Unfortunately, I have not been able to find an elegant solution for this problem. What I'm doing right now seems horrible to me (indirections etc...):
n = 4;
x = Table[RandomReal, n]
{0.547984, 0.601967, 0.000917483, 0.738287}
Map[f[Apply[Sequence, x[[#]]]] &,
Flatten[Table[{i, j}, {i, 1, n}, {j, i + 1, n}], 1]]
{f[0.547984, 0.601967], f[0.547984, 0.000917483], f[0.547984,
0.738287], f[0.601967, 0.000917483], f[0.601967, 0.738287], f[0.000917483, 0.738287]}
(in real situation f is defined f[xi_,xj_]:= xi-xj for instance)
Question: what is a better (builtin?) solution?
list-manipulation programming
asked May 28 at 11:14
Picaud VincentPicaud Vincent
1,5827 silver badges18 bronze badges
$endgroup$
I am often facing the situation where I have a list ${...x_k...}$ and where I want to compute:
$$
{...f[x_i,x_j]...}text{ with } i<j
$$
Unfortunately, I have not been able to find an elegant solution for this problem. What I'm doing right now seems horrible to me (indirections etc...):
n = 4;
x = Table[RandomReal, n]
{0.547984, 0.601967, 0.000917483, 0.738287}
Map[f[Apply[Sequence, x[[#]]]] &,
Flatten[Table[{i, j}, {i, 1, n}, {j, i + 1, n}], 1]]
{f[0.547984, 0.601967], f[0.547984, 0.000917483], f[0.547984,
0.738287], f[0.601967, 0.000917483], f[0.601967, 0.738287], f[0.000917483, 0.738287]}
(in real situation f is defined f[xi_,xj_]:= xi-xj for instance)
Question: what is a better (builtin?) solution?
list-manipulation programming
list-manipulation programming
asked May 28 at 11:14
Picaud VincentPicaud Vincent
1,5827 silver badges18 bronze badges
asked May 28 at 11:14
Picaud VincentPicaud Vincent
1,5827 silver badges18 bronze badges
edited May 28 at 11:40
Picaud Vincent
asked May 28 at 11:14
Picaud VincentPicaud Vincent
1,5827 silver badges18 bronze badges
asked May 28 at 11:14
Picaud VincentPicaud Vincent
1,5827 silver badges18 bronze badges
asked May 28 at 11:14
Picaud VincentPicaud Vincent
1,5827 silver badges18 bronze badges
1,5827 silver badges18 bronze badges
add a comment
|
add a comment
|
1 Answer
1
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$begingroup$
Subsets[f @@ x, {2}]
{f[0.817389, 0.11142], f[0.817389, 0.789526], f[0.817389, 0.187803],
f[0.11142, 0.789526], f[0.11142, 0.187803], f[0.789526, 0.187803]}
You can also use
f @@@ Subsets[x, {2}]
Join @@ Table[f @@ x[[{i, j}]], {i, 1, n}, {j, i + 1, n}]
answered May 28 at 11:32
kglrkglr
221k10 gold badges251 silver badges508 bronze badges
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Subsets[f @@ x, {2}]
{f[0.817389, 0.11142], f[0.817389, 0.789526], f[0.817389, 0.187803],
f[0.11142, 0.789526], f[0.11142, 0.187803], f[0.789526, 0.187803]}
You can also use
f @@@ Subsets[x, {2}]
Join @@ Table[f @@ x[[{i, j}]], {i, 1, n}, {j, i + 1, n}]
answered May 28 at 11:32
kglrkglr
221k10 gold badges251 silver badges508 bronze badges
$endgroup$
add a comment
|
$begingroup$
Subsets[f @@ x, {2}]
{f[0.817389, 0.11142], f[0.817389, 0.789526], f[0.817389, 0.187803],
f[0.11142, 0.789526], f[0.11142, 0.187803], f[0.789526, 0.187803]}
You can also use
f @@@ Subsets[x, {2}]
Join @@ Table[f @@ x[[{i, j}]], {i, 1, n}, {j, i + 1, n}]
answered May 28 at 11:32
kglrkglr
221k10 gold badges251 silver badges508 bronze badges
$endgroup$
add a comment
|
$begingroup$
Subsets[f @@ x, {2}]
{f[0.817389, 0.11142], f[0.817389, 0.789526], f[0.817389, 0.187803],
f[0.11142, 0.789526], f[0.11142, 0.187803], f[0.789526, 0.187803]}
You can also use
f @@@ Subsets[x, {2}]
Join @@ Table[f @@ x[[{i, j}]], {i, 1, n}, {j, i + 1, n}]
answered May 28 at 11:32
kglrkglr
221k10 gold badges251 silver badges508 bronze badges
$endgroup$
Subsets[f @@ x, {2}]
{f[0.817389, 0.11142], f[0.817389, 0.789526], f[0.817389, 0.187803],
f[0.11142, 0.789526], f[0.11142, 0.187803], f[0.789526, 0.187803]}
You can also use
f @@@ Subsets[x, {2}]
Join @@ Table[f @@ x[[{i, j}]], {i, 1, n}, {j, i + 1, n}]
answered May 28 at 11:32
kglrkglr
221k10 gold badges251 silver badges508 bronze badges
edited May 28 at 11:37
answered May 28 at 11:32
kglrkglr
221k10 gold badges251 silver badges508 bronze badges
answered May 28 at 11:32
kglrkglr
221k10 gold badges251 silver badges508 bronze badges
answered May 28 at 11:32
kglrkglr
221k10 gold badges251 silver badges508 bronze badges
221k10 gold badges251 silver badges508 bronze badges
add a comment
|
add a comment
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