Look up a value in an incomplete list

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clauper
clauper 2022-2-21
评论： DGM 2022-2-21
I have keys and values like this:
keys = ["a", "b", "c", "d"];
vals = [3,4,2,1];
and I need to look up the values for x, but not all keys exist, e.g.:
x = ["c", "d", "e"];
which should result in:
y = [2, 1, NaN];
The problem I have is that strfind(), matches() yield empty arrays for "e", which leads to errors when looking up in vals.
Also, all arrays are >100k so I would like to avoid a for-loop.

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采纳的回答

Stephen23
Stephen23 2022-2-21
编辑：Stephen23 2022-2-21
Ran in:
Simpler and more efficient:
keys = ["a","b","c","d"];
vals = [3,4,2,1];
x = ["c","d","e"];
[idx,idy] = ismember(x,keys);
out = nan(size(x));
out(idx) = vals(idy(idx))
out = 1×3
2 1 NaN

更多回答（2 个）

DGM
DGM 2022-2-21
Ran in:
How about:
keys = ["a", "b", "c", "d"];
vals = [1,2,3,4];
x = ["c", "d", "e"];
[~,y] = ismember(x,keys);
y(y==0) = NaN
y = 1×3
3 4 NaN
  2 个评论
clauper
clauper 2022-2-21
编辑：clauper 2022-2-21
This looks promising. However, I need the values in vals, not the indices. I changed vals in the question such that the two can be distinguished.
DGM
DGM 2022-2-21
Ran in:
Oof. I forgot about that.
keys = ["a", "b", "c", "d"];
vals = [11,22,33,44];
x = ["c", "d", "e"];
[m idx] = ismember(x,keys);
y = NaN(size(m));
y(m) = vals(idx(m))
y = 1×3
33 44 NaN

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clauper
clauper 2022-2-21
Ran in:
I figured it out:
keys = ["a", "b", "c", "d"];
vals = [3,4,2,1];
x = ["c", "d", "e"];
[~, idx] = ismember(x, keys);
keyExists = matches(x, keys);
y = nan(length(x),1);
y(keyExists) = vals(idx(idx~=0))
y = 3×1
2 1 NaN
I don't know if there is a more efficient way but this works.

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