How to lookup and return a corresponding value from table?

I have a table the first column of which contains a string and other columns contain numeric data, how do I match the string and return the corresponding values form other columns for this string. Lets say for 'obs2' I want '2' as output. I am using following code but this isn't working.

cmnt0 = {'obs1';'obs2';'obs3';'obs4'};
curve=[1;2;3;2];
cmnt1 = table(cmnt0,curve,'VariableNames',{'obs','Curve'})

cmnt1 = 4×2 table
      obs       Curve
    ________    _____

    {'obs1'}      1  
    {'obs2'}      2  
    {'obs3'}      3  
    {'obs4'}      2  

for i=[1,2,3,4]
    x=strcmp(cmnt1(i,1),'obs1')
    if x==1
    %% some code here after that
    end
end

x = logical
   0

x = logical
   0

x = logical
   0

x = logical
   0

Answer 1

[Voss]

It isn't working because cmnt1(i,1) is a sub-table of the table cmnt1 that contains one cell of cmnt1. You want to refer to the contents of the cell directly, so use curly brace indexing:

cmnt0 = {'obs1';'obs2';'obs3';'obs4'};
curve=[1;2;3;2];
cmnt1 = table(cmnt0,curve,'VariableNames',{'obs','Curve'})

cmnt1 = 4×2 table
      obs       Curve
    ________    _____

    {'obs1'}      1  
    {'obs2'}      2  
    {'obs3'}      3  
    {'obs4'}      2  

% introduce a third column for demonstration:
cmnt1.Curve_2 = [5;6;7;8]

cmnt1 = 4×3 table
      obs       Curve    Curve_2
    ________    _____    _______

    {'obs1'}      1         5   
    {'obs2'}      2         6   
    {'obs3'}      3         7   
    {'obs4'}      2         8   

for i=[1,2,3,4]
%     x=strcmp(cmnt1(i,1),'obs1')
    x=strcmp(cmnt1{i,1},'obs1')
    if x==1
    %% some code here after that
        output = cmnt1{i,2:end} % do this to store the contents of the cells in columns 2 to the end (which are all numeric), or
        output = cmnt1{i,2} % do this to store the contents of the cell in column 2
    end
end

x = logical
   1

output = 1×2

1 5

output = 1

x = logical
   0

x = logical
   0

x = logical
   0

You can do the same thing without a loop, using logical indexing, which is intended to also handle the situation where the string you are matching occurs more than once in the first column of the table:

% introduce a second 'obs1':
cmnt1{3,1} = {'obs1'}

cmnt1 = 4×3 table
      obs       Curve    Curve_2
    ________    _____    _______

    {'obs1'}      1         5   
    {'obs2'}      2         6   
    {'obs1'}      3         7   
    {'obs4'}      2         8   

is_match = strcmp(cmnt1{:,1},'obs1')

is_match = 4×1 logical array
   1
   0
   1
   0

output_array = cmnt1{is_match,2:end}

output_array = 2×2

1 5 3 7

output_subtable = cmnt1(is_match,2:end)

output_subtable = 2×2 table
    Curve    Curve_2
    _____    _______

      1         5   
      3         7   

[deepak kumar]

thank you for support. Your answer helped.

But containers.Map are the exact thing I was looking for.

Answer 2

[dpb]

I'd start by turning 'obs' into a categorical variable...

cmnt0 = categorical({'obs1';'obs2';'obs3';'obs4'});
curve=[1;2;3;2];
tC = table(cmnt0,curve,'VariableNames',{'Obs','Curve'});
...
C=t.Curve(t.Obs=='Obs1');

Alternatively, if there is some reason to not create the categorical variable, then

C=t.Curve(contains(t.Obs,{'Obs1'}));

With such a data set, I'd suggest you'll find that groupsummary and/or rowfun and friends with grouping variables will solve virtually all such problems almost automagically.

[Stephen23]

One reason to avoid CONTAINS will be clear once the data set includes OBS10, etc.

For robust code, use STRCMP or STRCMPI.

[Steven Lord]

I would probably use matches instead of strcmp or strcmpi.

matches(["ab1"; "ab10"], "ab1")

ans = 2×1 logical array
   1
   0

[dpb]

" avoid CONTAINS..."

Good point...why I would use categorical variables here.