Find matched string in table

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The Finnish Rein Deer
评论： The Finnish Rein Deer 2020-3-11
Hi,
To find data matching certain conditions in a table we use:
rows = (T.Smoker==true & T.Age<40);
What if the T.Smoker field was not a logical but a string? 'yes' or 'no'.
rows = (T.Smoker=='yes' & T.Age<40);
This later code does not work. How could I make it work so the condition matches a certain string?
Thank you,
TD

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采纳的回答

Steven Lord
Steven Lord 2020-3-9
Compare the text data stored in the table with a string array. Let's build a sample using the example from the documentation for the table function.
load patients
patients = table(LastName,Gender,Age,Height,Weight,Smoker,Systolic,Diastolic);
Let's extract patients under 40, separated by gender.
malePatientsUnder40 = patients(patients.Gender == "Male" & patients.Age < 40, :)
femalePatientsUnder40 = patients(patients.Gender == "Female" & patients.Age < 40, :)
Let's check against the full list of patients under 40.
patientsUnder40 = patients(patients.Age < 40, :);
Combine the male and female patients into one larger table and compare it against the full list.
isequal(sortrows([malePatientsUnder40; femalePatientsUnder40]), sortrows(patientsUnder40))
  4 个评论
显示 2更早的评论
Steven Lord
Steven Lord 2020-3-10
If you build the patients table using the patients.mat file the Gender variable is actually a cellstr, a cell array containing char vectors. It's not a string array, though you could use the cellstr to make one.
Comparing char arrays with string or categorical arrays we try to do "the nice thing" and and treat the text more like "words" rather than "bunches of characters". See this documentation page for a discussion about comparing char and string arrays and this one for char and categorical.
How would these work? Let's rebuild the patients table.
load patients
patients = table(LastName,Gender,Age,Height,Weight,Smoker,Systolic,Diastolic);
What type is the Gender variable in patients? It's a cellstr.
class(patients.Gender)
iscellstr(patients.Gender)
Since in this data set Gender only takes two values, we can store and display them as two categories using a categorical array. We can match a categorical array using a char vector, a string, or a categorical value. [I'm switching the Age threshold to 30 just so the filtered table arrays are shorter.]
patients.GenderCat = categorical(patients.Gender);
F1 = patients(patients.GenderCat == 'Female' & patients.Age < 30, :)
F2 = patients(patients.GenderCat == "Female" & patients.Age < 30, :)
FCategory = patients.GenderCat(3) % The first Female patient is in row 3
F3 = patients(patients.GenderCat == FCategory & patients.Age < 30, :)
Or you can turn that cellstr data into string.
patients.GenderStr = string(patients.Gender);
F4 = patients(patients.GenderStr == "Female" & patients.Age < 30, :)
F5 = patients(patients.GenderStr == 'Female' & patients.Age < 30, :)

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更多回答（2 个）

Fangjun Jiang
Fangjun Jiang 2020-3-9
isequal(T.Smoker, 'yes')
strcmpi(T.Smoker, 'yes')
  1 个评论
The Finnish Rein Deer
The Finnish Rein Deer 2020-3-10
Thanks. Isequal does not work, and strcmpi is better to replace for strcmp, since the former would match independently of case.

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Image Analyst
Image Analyst 2020-3-9
Try contains:
rows = contains(T.Smoker, 'yes') & T.Age<40;
  1 个评论
The Finnish Rein Deer
The Finnish Rein Deer 2020-3-10
Actually, I realized that the code I suggested would work if only I had changed simple quotes for double ones!
rows = (T.Smoker=='yes' & T.Age<40); % does not work
rows = (T.Smoker=="yes" & T.Age<40); % does work

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