Print first few lines of output

Question

alpedhuez 2021-1-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/725252-print-first-few-lines-of-output

评论： Walter Roberson 2021-1-24

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Suppose I do

summary(T)

Then it will print out statistics of all the variables in the table, which is good. But at the same time it will output all the information and will create "auto-scroll" that is very cumbersome. Thus I want to print out the first five lines of the output.

head(summary(T),5)

does not work.

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Answer 1

Walter Roberson 2021-1-23

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https://ww2.mathworks.cn/matlabcentral/answers/725252-print-first-few-lines-of-output#answer_604737

编辑：Walter Roberson 2021-1-23

在 MATLAB Online 中打开

summary(T(:,1))

If summary() was just being used as an example, then

temp = regexp(evalc("Put The Command Here"), '\n', 'split');
fprintf('%s\n', temp{1:min(end,5)});

such as

temp = regexp(evalc("summary(T)"), '\n', 'split');
fprintf('%s\n', temp{1:min(end,5)});

You can build a function to do this for you.

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Walter Roberson 2021-1-24

在 MATLAB Online 中打开

T = table(randn(20,1), rand(20,1)*5-2);
summary(T)
Variables:

    Var1: 20x1 double

        Values:

            Min       -2.9423 
            Median    0.25113 
            Max        1.7915 

    Var2: 20x1 double

        Values:

            Min       -1.8869 
            Median     1.0298 
            Max        2.9588 
summary(T(:,1))
Variables:

    Var1: 20x1 double

        Values:

            Min       -2.9423 
            Median    0.25113 
            Max        1.7915 

First 5 lines of summary(T) are:

Variables:
Var1: 20x1 double
Values:

The only useful information there is Var1: 20x1 double . Which you could get by

size(T{:,1}), class(T{:,1})
ans = 1×2
    20     1
ans = 'double'

If you compare the first group of summary(T) to the first group of summary(T(:,1)) you will see they are the same. The result is not the summary of the first rows of T: the result is the first (useful) output group of summary(T)

Perhaps I need to make an explicit statement:

There is no built-in function that will provide the first N lines of output of a command given as an argument such as you show for

head(summary(T),5)

Furthermore, it is impossible to write such a thing in MATLAB, as MATLAB always executes parameters completely first before executing the enclosing function, so the summary(T) would be executed first, in a context in which it would be informed that it was expected to return one output. When summary(T) is executed in a context in which it is expected to return one output, it returns a struct array, not printed output.

There is also no built-in function that you can pass a string or character vector argument to and it will return the first given number of lines of it. That is at least possible in MATLAB: it just has not been done. However, you can write it yourself.

Walter Roberson 2021-1-24

在 MATLAB Online 中打开

T = table(randn(20,1), rand(20,1)*5-2);
HEAD('summary(T)', 8)
Variables:

    Var1: 20x1 double

        Values:

            Min       -1.6334 
HEAD('T+1', 4)
Error using evalin
Undefined function 'plus' for input arguments of type 'table'.

Error in LiveEditorEvaluationHelperEeditorId>HEAD (line 10)
function details___ = HEAD(COMMAND__, N__)
  if nargin < 2; N__ = 5; end
  try
      CMD__ = "evalin('caller', '" + COMMAND__ + "')";
      details__ = evalc(CMD__);
  catch ME__
      details__ = getReport(ME__);
  end
  detail_lines = regexp(details__, '\n', 'split');
  details__ = strjoin(detail_lines(1:min(N__,end)), '\n');
  if nargout == 0
      disp(details__);
  else
      details___ = details__;
  end
end

Walter Roberson 2021-1-24

Note that the code was designed so that if an error message is the output of the command, then only the first N lines of the error message are output.

The code is designed so that you can assign the output of HEAD() to a variable, but that if you do not do so then it outputs to the display.

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Print first few lines of output

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Print first few lines of output

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