grouping elements from a table

Question

eric capnu 2017-9-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/355643-grouping-elements-from-a-table

评论： eric capnu 2017-9-19

采纳的回答： Akira Agata

在 MATLAB Online 中打开

Hi everyone:

i have a table like this:

Week     Open       High       Low     Close
----     ----       ----       ---     -----
     1.2        1.4        1.1     1.2
     1.5        1.7        1.5     1.6
     1.4        2.1        1.3     2
     2.2        2.4        2       2.1
     2          2.1        2       2
     2.2        2.5        1.1     1.3
     1.7        1.9        1.6     1.6
     1.8        1.9        0.6     1.4
     0.9        1.4        0.8     1

is there a way to get the first element(open), maximum element(high), minimum element(low) and last element (close) for each week? so the result table would be

Week     Open       High       Low     Close
----     ----       ----       ---     -----
10       1.2        2.4        1.1     2.1
11       2          2.5        1.1     1.3
12       1.7        1.9        0.6     1

thanks in advance

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Akira Agata 2017-9-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/355643-grouping-elements-from-a-table#answer_280707

在 MATLAB Online 中打开

Assuming your table is T, the following code can generate what you want.

[group, id] = findgroups(T.Week);
func = @(p, q, r, s) [p(1), max(q), min(r), s(end)];
result = splitapply(func, T.Open, T.High, T.Low, T.Close, group)
Tout = array2table([id, result],...
  'VariableNames', T.Properties.VariableNames);

3 个评论
显示 1更早的评论隐藏 1更早的评论

Walter Roberson 2017-9-18

在 MATLAB Online 中打开

>> findgroups([1 2.5 2 2.5 1])
ans =
     1     3     2     3     1

Looks like it works for double to me.

eric capnu 2017-9-19

my mistake, i was working on a 2014 matlab version

请先登录，再进行评论。

Answer 2

Guillaume 2017-9-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/355643-grouping-elements-from-a-table#answer_280708

在 MATLAB Online 中打开

Step 1: define a function in its own m file that applies the appropriate filter to each column (unfortunately, you can't use anonymous functions for this):

function [firstopen, maxhigh, minlow, lastclose] = filtercols(open, high, low, close)
   firstopen = open(1);  %first element
   maxhigh = max(high);
   minlow = min(low);
   lastclose = close(end);  %last element
end

Step 2: use that function with rowfun

t = array2table([
     1.2        1.4        1.1     1.2
     1.5        1.7        1.5     1.6
     1.4        2.1        1.3     2
     2.2        2.4        2       2.1
     2          2.1        2       2
     2.2        2.5        1.1     1.3
     1.7        1.9        1.6     1.6
     1.8        1.9        0.6     1.4
     0.9        1.4        0.8     1], ...
'VariableNames', {'Week', 'Open', 'High', 'Low', 'Close'});
 result = rowfun(@filtercols, t, 'GroupingVariable', 'Week', 'NumOutputs', 4, 'OutputVariableNames', {'Open', 'High', 'Low', 'Close'})

The only potential issue is that the order in which the rows are grouped together by rowfun is not documented, so it may be that the first element and last element are not the correct ones. In my version of matlab (R2017a), it is correct.