joining string variables in a table with strjoin and rowfun

Hey all,

I'm trying to concatenate strings stored in table variables together using strjoin and rowfun. Seems liek this should be a pretty trivial problem, but I'm having trouble.

Here's what I'm trying to do

a = [1;2;3];
b = {'one'; 'two'; 'three'};
c = {'uno'; 'dos'; 'tres'};
T = table(a,b,c)

rowfun(@(aa, bb) {strjoin({aa,bb}, '_')}, T, 'InputVariables', {'b', 'c'})

This gives an error however:

Error using table/rowfun>dfltErrHandler (line 310)
Applying the function '@(aa,bb){strjoin({aa,bb},'_')}' to the 1st row of A generated the following
error:

First input must be a 1xN cell array of strings.


Error in table/rowfun>@(s,varargin)dfltErrHandler(grouped,funName,s,varargin{:}) (line 197)
    errHandler = @(s,varargin) dfltErrHandler(grouped,funName,s,varargin{:});

Error in table/rowfun (line 215)
                [b_data{i,:}] = errHandler(struct('identifier',ME.identifier, 'message',ME.message,
                'index',i),inArgs{:});

The error ` First input must be a 1xN cell array of strings ` is clearly from strjoin not getting the right input, but I'm not sure why. I thought itm ight be my use of {} in the function so I rewrote it like this:

rowfun(@(aa, bb) {strjoin(cell(aa,bb), '_')}, T, 'InputVariables', {'b', 'c'})

But now it gives a different error:

'Conversion to double from cell is not possible.'

If I try to run it outside of rowfun I get the same errors

catFunc = @(aa, bb) strjoin(cell(aa,bb), '_')
catFunc(T.b(1), T.c(1))

What am I doing wrong here? I'm confused why the first version of the function doesn't work and strjoin isn't seeing a cell array of strings, and I'm confused why changing the {} in the function call to cell() changes the error I'm seeing

[Stephen23]

Using ROWFUN is like cracking a walnut with a sledgehammer. Simpler (even before the string class):

a = [1;2;3];
b = {'one'; 'two'; 'three'};
c = {'uno'; 'dos'; 'tres'};
T = table(a,b,c)

T = 3×3 table
    a        b           c    
    _    _________    ________

    1    {'one'  }    {'uno' }
    2    {'two'  }    {'dos' }
    3    {'three'}    {'tres'}

strcat(T.b,'_',T.c)

ans = 3×1 cell array
    {'one_uno'   }
    {'two_dos'   }
    {'three_tres'}

Answer 1

[Cris LaPierre]

Not super familiar with rowfun, so here's a simple way to get around it:

T.b = string(T.b);
T.c = string(T.c);
T.b + " " + T.c

ans = 
    "one uno"
    "two dos"
    "three tres"

[Emily T. Griffiths]

by far the more helpful answer

Answer 2

[per isakson]

Replace

rowfun(@(aa, bb) {strjoin({aa,bb}, '_')}, T, 'InputVariables', {'b', 'c'})

by

rowfun( @(aa,bb) {strjoin([aa,bb],'_')}, T, 'InputVariables', {'b','c'})

since aa and bb already are cell arrays. Then you get

ans =
  3×1 table
        Var1    
    ____________
    'one_uno'   
    'two_dos'   
    'three_tres'