Speed Up String Conversion
显示 更早的评论
Hi all. I am trying to speed up string conversion of a table field as below :-
GoingUC=string(table2cell(Inps(:,5)));
Inps is a table with approximately 730000 records with 13 fields. I've got 6 categorical fields to convert and it is taking over 2.5 hours so I wondered if there was a quicker way to do this. I need a string array for the following code which converts the categorical strings to numbers in a map (which is quick) :-
[Unique_GoingU,~,GoingU_Numeric_Cats] = unique(GoingUC);
CTNM_GoingU=containers.Map(Unique_GoingU,num2cell(1:length(Unique_GoingU)));
NTD_GoingU=cell2mat(values(CTNM_GoingU,num2cell(GoingUC)));
It all works perfectly for my use but it's just if I can speed it up that would be great.
Steve Gray
2 个评论
The third output from unique is the same as the end result (or the transpose of the end result, if GoingUC is a row vector), so using a Map is unnecessary.
GoingUC = string(randi(10,10000,1))
[Unique_GoingU,~,GoingU_Numeric_Cats] = unique(GoingUC)
CTNM_GoingU=containers.Map(Unique_GoingU,num2cell(1:length(Unique_GoingU)));
NTD_GoingU=cell2mat(values(CTNM_GoingU,num2cell(GoingUC)))
isequal(GoingU_Numeric_Cats,NTD_GoingU)
Stephen Gray
2024-5-1
采纳的回答
Avoid using table2cell for this; instead, access the table data directly (using curly braces {}, or, even better, dot indexing)
% 100000x1 table of categoricals
Inps = table(categorical(randi(10,100000,1)))
% using table2cell
tic
str1 = string(table2cell(Inps(:,1)));
toc
% using curly brace indexing
tic
str2 = string(Inps{:,1});
toc
% using dot indexing
tic
str3 = string(Inps.(1));
toc
Accessing the table data directly is > 100 times faster, and produces the same result:
isequal(str2,str2,str3)
3 个评论
Stephen Gray
2024-5-1
You're welcome!
table2cell could be useful for collecting multiple variables of a table into a cell array, particularly if the variables contain different classes of data. Although I would most likely just keep the data in table form.
T = table(rand(10,1),cellstr(char(65+randi([0,9],10,5))),string(rand(10,1)))
% table to cell keeps the data classes as they are in the table
C = table2cell(T(:,[1 2 3]))
% but the concatenation required when accessing directly converts
% numeric and cell char to string, in order to combine the
% numeric and cell char table variables with the string variable
T{:,[1 2 3]}
C = [T.(1) T.(2) T.(3)]
Stephen Gray
2024-5-1
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Tables 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
