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Modified subindex to be faster. Note also changed behavior for

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idx=singleton list.
This commit is contained in:
Adrian Mariano 2020-08-02 10:35:32 -04:00
parent 47d02ae783
commit 37ca6efebb
1 changed files with 15 additions and 15 deletions
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30
arrays.scad
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@ -1172,25 +1172,25 @@ function add_scalar(v,s) =
// Function: subindex()
// Usage:
// subindex(M, idx)
// Description:
// For each array item, return the indexed subitem.
// Returns a list of the values of each vector at the specfied
// index list or range. If the index list or range has
// only one entry the output list is flattened.
// Extracts the entries listed in idx from each entry in M. For a matrix this means
// selecting a specified set of columsn. If idx is a number the return is a vector, otherwise
// it is a list of lists (the submatrix).
// Arguments:
// v = The given list of lists.
// M = The given list of lists.
// idx = The index, list of indices, or range of indices to fetch.
// Example:
// v = [[[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]];
// subindex(v,2); // Returns [3, 7, 11, 15]
// subindex(v,[2,1]); // Returns [[3, 2], [7, 6], [11, 10], [15, 14]]
// subindex(v,[1:3]); // Returns [[2, 3, 4], [6, 7, 8], [10, 11, 12], [14, 15, 16]]
function subindex(v, idx) =
[ for(val=v)
let( value=[for(i=idx) val[i]] )
len(value)==1 ? value[0] : value
];
// M = [[[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]];
// subindex(M,2); // Returns [3, 7, 11, 15]
// subindex(M,[2]); // Returns [[3], [7], [11], [15]]
// subindex(M,[2,1]); // Returns [[3, 2], [7, 6], [11, 10], [15, 14]]
// subindex(M,[1:3]); // Returns [[2, 3, 4], [6, 7, 8], [10, 11, 12], [14, 15, 16]]
function subindex(v, idx) =
is_num(idx)
? [for(row=M) row[idx]]
: [for(row=M) [for(i=idx) row[i]]];
// Function: zip()
// Usage: