Get mean and stdev from all values

Hi,

I have a list like below. in the first column I have values from 0 to 91 (there can miss values).

0	3
0	4.50000000000000
0	1.37500000000000
0	5
0	3
0	0.838961038961039
0	2.80000000000000
1	1.50000000000000
1	0.555555555555556
1	1.71428571428571
1	3.38666666666667
1	4
1	3.38666666666667
2	1.73684210526316
2	1
2	1.30769230769231
2	2.73333333333333
2	1
2	2

I want to calculate the mean and standard deviation for all of these values if they exist.

How can I realise this? Now I have the folowing:

clear all; clc; close all;
standaard = readmatrix('/Users/diontheunissen/Documents/Apployee/Smart_driver/avgFuel.xlsx');
indices = find(standaard(:,1)==0);
standaard(indices,:) = [];
indices = find(standaard(:,2)>8);
standaard(indices,:) = [];

standaard(:,1) = round(standaard(:,1));
standaard = sortrows(standaard,1);
c = {};
for i = 0:5:85
    if i == 0
    lower = find(standaard(:,1) == i);
    n = i+5;
    upper = find(standaard(:,1) == n);
    elseif i>1
    lower = find(standaard(:,1) == i+1);
    n = i+5;
    upper = find(standaard(:,1) == n);
    end
    tab = standaard(lower(1):upper(end),:);
    c{i+1} = tab;
end
referent2 = []
for j = 1:5:86
    data = cell2mat(c(j));

    referent(1,1) = data(1,1);
    referent(1,2) = mean(data(:,2));
    referent(1,3) = std(data(:,2));
    referent2 = [referent2;referent]
end

snelheid = linspace(min(referent2(:,1)),max(referent2(:,1))); 
a1 = interp1(referent2(:,1), referent2(:,2:end), snelheid, 'makima');
verbruik = a1(:,1);
upper = a1(:,1)+a1(:,2);
lower = a1(:,1)-a1(:,2);

figure

hold on 
plot(snelheid, verbruik, '-b');
plot(snelheid, upper,'-r');
plot(snelheid, lower,'-g');

How can i change this script that i get the mean and stdev from all existing values?

thanks

[DGM]

Can you clarify the structure of the file and what you're trying to do? I'm assuming you're trying to find the blockwise mean and std for column 2, the blocks being described by column 1. Are all blocks the same size? Are the values in column 1 sorted?

[Dion Theunissen]

Indeed, the blocks have not the same size and are sorted in column 1.

So i need to check for each value from 1 untill 91 the mean and standard deviation

Answer 1

[DGM]

If column 1 is sorted:

% build test array
idx = repelem(1:10,randi(6,10,1));
idx = idx(1:20);
D = [idx.' rand(20,1)]; % the test array

% find length of blocks
blocklengths = diff([0 find(diff(idx)) numel(idx)]);

% split and process
C = mat2cell(D(:,2),blocklengths,1);
bkmean = cellfun(@mean,C)

bkmean = 6×1

0.8030 0.6236 0.4651 0.2942 0.4628 0.6299

bkstd = cellfun(@std,C)

bkstd = 6×1

0.1993 0.3422 0.1443 0.2592 0.5516 0.0849

Answer 2

[Stephan]

Use a table and then use findgroups combined with splitappy. This will allow you to solve the problem with a few lines of code. This will also work if the columns are not sorted.

[Steven Lord]

findgroups can operate on numeric data as well as tabular data.

But rather than call those two functions sequentially, I'd probably just use groupsummary.

X = [0	3;
0	4.50000000000000;
0	1.37500000000000;
0	5;
0	3;
0	0.838961038961039;
0	2.80000000000000;
1	1.50000000000000;
1	0.555555555555556;
1	1.71428571428571;
1	3.38666666666667;
1	4;
1	3.38666666666667;
2	1.73684210526316;
2	1;
2	1.30769230769231;
2	2.73333333333333;
2	1;
2	2];
[M, BG] = groupsummary(X(:, 2), X(:, 1), @mean)

M = 3×1

2.9306 2.4239 1.6296

BG = 3×1

0 1 2

check = mean(X(X(:, 1)== 1, 2)) % This is the same as M(BG == 1)

check = 2.4239

S = groupsummary(X(:, 2), X(:, 1), @std)

S = 3×1

1.5037 1.3554 0.6728

MS = groupsummary(X(:, 2), X(:, 1), {@mean, @std}) % Compute M and S simultaneously

MS = 3×2

2.9306 1.5037 2.4239 1.3554 1.6296 0.6728