Matlab strcmp Error - help

Question

Prathamesh Halagi 2020-12-24

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评论： dpb 2020-12-25

采纳的回答： dpb

Table_3.mat

在 MATLAB Online 中打开

Hello,

I am trying to write a code where I need to export a table from excel, later I want to get the value in column named 'IR' if the value in column 'Current' is less than -70.00. I did use strcmp earlier in other places where it worked well but it shows error when I use it for this part. The follwing is my script:

clear
clc
opts = detectImportOptions('DCIR2.xls', 'Sheet','sheet2','Range', 'A1:G21'); 
opts.SelectedVariableNames = opts.SelectedVariableNames([3, 5, 7]);  
Table_3 = readtable('DCIR2.xls', opts);
DCIR = Table_3{strcmp(Table_3{:, 'Current'} '< -135'), 'IR'};

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Answer 1

dpb 2020-12-24

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The biggest problem is you're trying to deal with numeric data as string -- convert to numeric. This, unfortunately, isn't handled at all well by MATLAB out of the box when using European conventions as MATLAB ignores the user locale setting for numeric values. This is, in this day and age, truly embarrassing for TMW imo.

However, for simple cases like this, it's easy enough to work around...

>> load Table_3     % load the example table; see what looks like...
>> head(Table_3)
ans =
  8×7 table
        StepID         StepID_1       Voltage      Voltage_1       Current       Current_1       IR    
    ______________    ___________    __________    __________    ____________    _________    _________
    {'2 CC_DChg' }    {'3 Rest' }    {'4,0057'}    {'4,0848'}    {'-135,993'}      0.00       {'0,582'}
    {'5 CC_DChg' }    {'6 Rest' }    {'3,9434'}    {'4,0042'}    {'-67,969' }      0.00       {'0,895'}
    {'7 CC_DChg' }    {'8 Rest' }    {'3,9124'}    {'3,9955'}    {'-135,956'}      0.00       {'0,611'}
    {'10 CC_DChg'}    {'11 Rest'}    {'3,8581'}    {'3,9245'}    {'-67,987' }      0.00       {'0,977'}
    {'12 CC_DChg'}    {'13 Rest'}    {'3,8284'}    {'3,9155'}    {'-136,012'}      0.00       {'0,64' }
    {'15 CC_DChg'}    {'16 Rest'}    {'3,7701'}    {'3,851' }    {'-67,987' }      0.00       {'1,19' }
    {'17 CC_DChg'}    {'18 Rest'}    {'3,7506'}    {'3,8392'}    {'-135,956'}      0.00       {'0,652'}
    {'20 CC_DChg'}    {'21 Rest'}    {'3,6845'}    {'3,7478'}    {'-67,969' }      0.00       {'0,931'}
>> 
>> Table_3.IR=str2double(strrep(Table_3.IR,',','.'));  % convert the IR variable to numeric; swap '.' for ',' to do so
>> head(Table_3)                                       % now see what that looks like...
ans =
  8×7 table
        StepID         StepID_1       Voltage      Voltage_1       Current       Current_1     IR 
    ______________    ___________    __________    __________    ____________    _________    ____
    {'2 CC_DChg' }    {'3 Rest' }    {'4,0057'}    {'4,0848'}    {'-135,993'}      0.00       0.58
    {'5 CC_DChg' }    {'6 Rest' }    {'3,9434'}    {'4,0042'}    {'-67,969' }      0.00       0.90
    {'7 CC_DChg' }    {'8 Rest' }    {'3,9124'}    {'3,9955'}    {'-135,956'}      0.00       0.61
    {'10 CC_DChg'}    {'11 Rest'}    {'3,8581'}    {'3,9245'}    {'-67,987' }      0.00       0.98
    {'12 CC_DChg'}    {'13 Rest'}    {'3,8284'}    {'3,9155'}    {'-136,012'}      0.00       0.64
    {'15 CC_DChg'}    {'16 Rest'}    {'3,7701'}    {'3,851' }    {'-67,987' }      0.00       1.19
    {'17 CC_DChg'}    {'18 Rest'}    {'3,7506'}    {'3,8392'}    {'-135,956'}      0.00       0.65
    {'20 CC_DChg'}    {'21 Rest'}    {'3,6845'}    {'3,7478'}    {'-67,969' }      0.00       0.93
>> Table_3.StepID=categorical(Table_3.StepID);      % also, the ID variables are categorical...convert
>> head(Table_3)
ans =
  8×7 table
      StepID       StepID_1       Voltage      Voltage_1       Current       Current_1     IR 
    __________    ___________    __________    __________    ____________    _________    ____
    2 CC_DChg     {'3 Rest' }    {'4,0057'}    {'4,0848'}    {'-135,993'}      0.00       0.58
    5 CC_DChg     {'6 Rest' }    {'3,9434'}    {'4,0042'}    {'-67,969' }      0.00       0.90
    7 CC_DChg     {'8 Rest' }    {'3,9124'}    {'3,9955'}    {'-135,956'}      0.00       0.61
    10 CC_DChg    {'11 Rest'}    {'3,8581'}    {'3,9245'}    {'-67,987' }      0.00       0.98
    12 CC_DChg    {'13 Rest'}    {'3,8284'}    {'3,9155'}    {'-136,012'}      0.00       0.64
    15 CC_DChg    {'16 Rest'}    {'3,7701'}    {'3,851' }    {'-67,987' }      0.00       1.19
    17 CC_DChg    {'18 Rest'}    {'3,7506'}    {'3,8392'}    {'-135,956'}      0.00       0.65
    20 CC_DChg    {'21 Rest'}    {'3,6845'}    {'3,7478'}    {'-67,969' }      0.00       0.93
>> 

The rest should be apparent to finish cleaning up the table; then you can use the data as numeric and direct numeric comparisons for the logic tests. Text comparisons of straight numeric float strings won't work for relational numeric comparisons; that's doing a strict lexical comparison, not numeric.

There is a way to work around the MATLAB limitations in a more generic fashion but it takes more work up front -- see Yair Altman's undocumented site at <Formatting-numbers> for using the Java engine instead that is locale aware.

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Steven Lord 2020-12-25

The biggest problem is you're trying to deal with numeric data as string -- convert to numeric. This, unfortunately, isn't handled at all well by MATLAB out of the box when using European conventions as MATLAB ignores the user locale setting for numeric values. This is, in this day and age, truly embarrassing for TMW imo.

If you're using detectImportOptions you can specify the 'DecimalSeparator' option either in the detectImportOptions call itself or using setvaropts after the import options object has been created. The 'ThousandsSeparator' option may also be of interest.

dpb 2020-12-25

Thanks for the heads-up, Steven...I had looked thinking should be there and somehow missed seeing it...which release incorporated the feature, you remember? (Not convenient to open ML at the moment).

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