Select row from matrix based on month with datenum

Hi. I have 2 matrices. A(12x1) contains month averages(Jan-Dec) and B(437x14) which contains daily values for specific days from 2007-2016. column 1 of matrix B contains datenum values. Is it possible to select a row from B if the value in column 9 is less than the corresponding monthly average from A.

For example: A(1,1) is for January and the average is 227.24. B(1,1) is 2/01/2006 and B(1,9) is 226.01. Then I would want to select that row and create a new matrix containing it as it is less than the corresponding monthly average.

Answer 1

[Andrei Bobrov]

Please attach file with your datas (A and B):

out = B(A(month(datetime(B(:,1),'InputFormat','yyyy-MM-dd'))) > B(:,9),:);

Answer 2

[Peter Perkins]

Andrei's solution also works out nicely with timetables:

>> monthlyAvg = timetable(rand(3,1),'RowTimes',datetime(2017,1:3,1,'Format','MMM-yyyy')')
monthlyAvg =
  3×1 timetable
      Time        Var1  
    ________    ________
    Jan-2017    0.078169
    Feb-2017     0.38762
    Mar-2017     0.17663
>> dailyData = timetable(rand(90,1),'RowTimes',datetime(2017,1,1:90)')
dailyData =
  90×1 timetable
        Time         Var1   
    ___________    _________
    01-Jan-2017      0.66487
    02-Jan-2017      0.65827
[snip]
    30-Mar-2017      0.11071
    31-Mar-2017      0.64954
>> dayToMonth = dailyData.Time.Month
dayToMonth =
     1
     1
[snip]
     3
     3
>> prunedData = dailyData(dailyData.Var1 < monthlyAvg.Var1(dayToMonth),:)
prunedData =
  20×1 timetable
        Time         Var1   
    ___________    _________
    15-Jan-2017     0.018667
    02-Feb-2017     0.056749
    05-Feb-2017      0.30348
    06-Feb-2017     0.050802
    08-Feb-2017      0.14254
    12-Feb-2017     0.052114
    14-Feb-2017       0.1085
    16-Feb-2017      0.37547
    19-Feb-2017      0.05188
    21-Feb-2017      0.17325
    26-Feb-2017      0.18982
    28-Feb-2017      0.29788
    03-Mar-2017      0.13819
    05-Mar-2017     0.090778
    10-Mar-2017      0.12096
    14-Mar-2017     0.069508
    16-Mar-2017      0.13549
    21-Mar-2017       0.0411
    29-Mar-2017    0.0070522
    30-Mar-2017      0.11071