Is it possible to use vertcat with dot notation?

EDITED Is it possible to use vertcat with dot notation?

This is an example once I extract names from Excel files contained in a folder:

%input
filename = dir(fullfile(directory,'*file*'));

% output
>> filename

filename = 

  3×1 struct array with fields:

    name
    folder
    date
    bytes
    isdir
    datenum

>> filename.name

ans =

    'file_1.xlsx'


ans =

    'file_2.xlsx'


ans =

    'file_3.xlsx'

% try to concatenate vertically the three files' names
>> vertcat(filename{:}.name)
Brace indexing is not supported for variables of this type.

[Jiri Hajek]

Hi, it's not clear, what type data is on your filename. Also the error is related to the fact that you are using braces for the filename, not for the vertcat...

[DGM]

@Jiri Hajek is correct. The error is being caused by the fact that filename is not a struct. Depending on how it was created, it may be empty, a char, a cell, or something else in certain degenerate cases. You'll have to check why it's becoming something other than a struct and safeguard against that case.

For example, if you're using dir() to find a file or the contents of a directory, does the query actually return any results? Does it return more than one result?

[Sim]

Thanks both @Jiri Hajek AND @DGM for your comments! I tried to add more information about what I did..please see the edited question :-)

[Jonas]

i gues you wanted

{filename.name}

[Sim]

@Jonas Yes! I feel extremely dumb in this moment ahahahaha :-) Sorry to everyone for my stupid question :-)

[Jiri Hajek]

Ok, you can put the names into a single variable, but considering the number of characters in each may be different, the most natural choice is cell array (column):

fileNameColumn = {filename.name}';

[Sim]

I am extremely thankful to all of you @Jiri Hajek @DGM @Jonas @Stephen23 for your comments (cool explanation @Stephen23!).... and at the same time, really sorry for my very silly question.... I did not think at all about {filename.name}... sorry! (In any case, if any of you wants to put your comments in the Answer section I will accept it with pleasure :-) )

Answer 1

[Stephen23]

"The error is being caused by the fact that filename is not a struct."

FILENAME is a struct (as returned by DIR). Curly brace indexing is not defined for structures (see the error message).

"Is it possible to use vertcat with dot notation?"

Of course, you can use any comma-separated list as the inputs to VERTCAT:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them

S = struct('X',{'hello','world'}) % content have same number of columns...

S = 1×2 struct array with fields:
    X

vertcat(S.X) % so VERTCAT is possible but fragile. Creates a character matrix.

ans = 2×5 char array
    'hello'
    'world'

But I would not recommend it because it is very fragile code: using VERTCAT on the structure from DIR() assumes that all of the filenames have exactly the same length, otherwise your code will throw an error:

S = struct('X',{'a','bcd'}) % content have different number of columns...

S = 1×2 struct array with fields:
    X

vertcat(S.X) % which is why VERTCAT is a bad approach.

Error using vertcat
Dimensions of arrays being concatenated are not consistent.

As Jonas correctly wrote, you should probably use a cell array: {filename.name}

Or, simply refer directly to the content of the structure array.

[Sim]

Thanks to all of you for your precious contribution @Stephen23, @Jonas, @Peter Perkins, @Jiri Hajek, @DGM.

Personally, I would have accepted all your answers/comments, but there is only the possibility to accept one. :-)

@MathWorks Support Team I think it might be nice (just an idea/suggestion) to have the possibility to accept multiple answers in some cases. :-)

Answer 2

[Peter Perkins]

Depending on what you are doing, you may find it convenient to turn that struct into a table (which wil automatically vertcat the file names for you):

s = dir

s = 2×1 struct array with fields:
    name
    folder
    date
    bytes
    isdir
    datenum

t = struct2table(s)

t = 2×6 table
     name                folder                         date              bytes    isdir     datenum  
    ______    ____________________________    ________________________    _____    _____    __________

    {'.' }    {'/users/mss.system.cHQNIJ'}    {'13-Dec-2022 16:06:16'}      0      true     7.3887e+05
    {'..'}    {'/users/mss.system.cHQNIJ'}    {'13-Dec-2022 16:06:16'}      0      true     7.3887e+05

[Stephen23]

"which wil automatically vertcat the file names for you"

Strictly speaking it creates a cell array of character arrays, rather than vertical concatenation of the field content:

S = dir();
T = struct2table(S)

T = 2×6 table
     name                folder                         date              bytes    isdir     datenum  
    ______    ____________________________    ________________________    _____    _____    __________

    {'.' }    {'/users/mss.system.rBKUO2'}    {'13-Dec-2022 16:16:37'}      0      true     7.3887e+05
    {'..'}    {'/users/mss.system.rBKUO2'}    {'13-Dec-2022 16:16:37'}      0      true     7.3887e+05

T.name % cell array, not vertical concatenation of char vectors.

ans = 2×1 cell array
    {'.' }
    {'..'}

[Sim]

Thanks to all of you for your precious contribution @Stephen23, @Jonas, @Peter Perkins, @Jiri Hajek, @DGM.

Personally, I would have accepted all your answers/comments, but there is only the possibility to accept one. :-)

@MathWorks Support Team I think it might be nice (just an idea/suggestion) to have the possibility to accept multiple answers in some cases. :-)

Answer 3

[Jonas]

if you just want to have all file names available, you could use { }

e.g. in a cell array

{filename.name}

if you do not need further information from the dir out beside the name, you could also abbreviate it to one line

{dir(fullfile(directory,'*file*')).name}

[Sim]

Thanks to all of you for your precious contribution @Stephen23, @Jonas, @Peter Perkins, @Jiri Hajek, @DGM.

Personally, I would have accepted all your answers/comments, but there is only the possibility to accept one. :-)

@MathWorks Support Team I think it might be nice (just an idea/suggestion) to have the possibility to accept multiple answers in some cases. :-)