How can I create a new column in a table via if function?

Question

Jennifer Pichl 2018-3-23

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评论： Jennifer Pichl 2018-3-26

I have a 45060x3 timetable, where the value kW ranges form 0 to 800. Now I want to create a new column (charger) which is definded by the if function down below. However when I execute this code, it creates a column (charger) where all the values equal the ones in kW even there are a lot of values which fullfill the if statement. Can you tell me what is the problem with this code? Or is there a other way to get the values I want for the new column?

if T3DHM18.kW<=400
   T3DHM18.charger=T3DHM18.kW+150  %%Take the values form T3DHM18.kW and add 150
else 
   T3DHM18.charger=T3DHM18.kW      %%if x>400 than it is same as T3DHM18.kW
end

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Answer 1

David Fletcher 2018-3-23

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By way of a smaller example -

%Create dummy table for the purpose of example
tbl=table()
tbl.KW=(1:10)'
%Copy KW column to a new charger column
tbl.Charger=tbl.KW
%Create indexer into the table for all rows where KW<4
ind=tbl.KW<4
%Add 150 to the rows where KW is less than 4
tbl.Charger(ind,:)=tbl.Charger(ind,:)+150

tbl =

10×2 table
    KW    Charger
    __    _______
  151    
  152    
  153    
    4    
    5    
    6    
    7    
    8    
    9    
   10

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Jennifer Pichl 2018-3-26

Thank you very much!

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Answer 2

Peter Perkins 2018-3-24

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https://ww2.mathworks.cn/matlabcentral/answers/390170-how-can-i-create-a-new-column-in-a-table-via-if-function#answer_311680

在 MATLAB Online 中打开

Another possibility, similar to David's solution:

T3DHM18.charger = T3DHM18.kW + 150*(T3DHM18.kW<=400)

The problem with the original code is that the if statement is written with element-wise assignment in mind, while the assignment itself is vectorized. When given a logical vector, an if statement evaluates only the first element (for historical reasons).