Trouble with date conversion

7 Nov 2023
3 Answers
Answer Accepted
Updated 10 Nov 2023
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I have a csv file in which the date is in the format YYYYMMDD for example 19910101 the nextr row has the hour. I cant manage to convert this tot three columns containing Year, month , day. Now I have imported the column als tekst How can I convert it to three Columns showing year, month day?
I dont have much experience with datasets yet.
the file is from the KNMI uurgeg_310_1991-2000.txt
%% Set up the Import Options and import the data
opts = delimitedTextImportOptions("NumVariables", 25);
% Specify range and delimiter
opts.DataLines = [34, Inf];
opts.Delimiter = ",";
% Specify column names and types
opts.VariableNames = ["Var1", "YYYYMMDD", "HH", "DD", "Var5", "FF", "Var7", "Var8", "Var9", "Var10", "Var11", "Var12", "Var13", "Var14", "P", "Var16", "Var17", "Var18", "Var19", "Var20", "Var21", "Var22", "Var23", "Var24", "Var25"];
opts.SelectedVariableNames = ["YYYYMMDD", "HH", "DD", "FF", "P"];
opts.VariableTypes = ["char", "char", "double", "double", "char", "double", "char", "char", "char", "char", "char", "char", "char", "char", "double", "char", "char", "char", "char", "char", "char", "char", "char", "char", "char"];
% Specify file level properties
opts.ExtraColumnsRule = "ignore";
opts.EmptyLineRule = "read";
% Specify variable properties
opts = setvaropts(opts, ["Var1", "YYYYMMDD", "Var5", "Var7", "Var8", "Var9", "Var10", "Var11", "Var12", "Var13", "Var14", "Var16", "Var17", "Var18", "Var19", "Var20", "Var21", "Var22", "Var23", "Var24", "Var25"], "WhitespaceRule", "preserve");
opts = setvaropts(opts, ["Var1", "YYYYMMDD", "Var5", "Var7", "Var8", "Var9", "Var10", "Var11", "Var12", "Var13", "Var14", "Var16", "Var17", "Var18", "Var19", "Var20", "Var21", "Var22", "Var23", "Var24", "Var25"], "EmptyFieldRule", "auto");
opts = setvaropts(opts, ["HH", "DD", "FF", "P"], "ThousandsSeparator", ",");
% Import the data
tbl = readtable("D:\01 werk in uitvoering\uurgeg_310_1991-2000.txt", opts);
%% Convert to output type
YYYYMMDD = tbl.YYYYMMDD;
HH = tbl.HH;
DD = tbl.DD;
FF = tbl.FF;
P = tbl.P;
%% Clear temporary variables
clear opts tbl

5 Comments
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Les Beckham
Les Beckham on 7 Nov 2023
If you attach your data file (use the paperclip icon in the INSERT section of the toolbar), you will be more likely to get help with this.
Stephen23
Stephen23 on 7 Nov 2023
"I cant manage to convert this tot three columns containing Year, month , day. Now I have imported the column als tekst"
Much better: import the date as a DATETIME object, then get the YEAR, MONTH, DAY property of that object:
https://www.mathworks.com/help/matlab/ref/datetime.html#d126e336703
Ellen
Ellen on 7 Nov 2023
Moved: Stephen23 on 7 Nov 2023
did you mean the csv file? I used the button import data, and changed the second column (from B34 to text) also tried with datetime but that did not work at al.
Ellen
Ellen
Ellen on 7 Nov 2023
When I Use datetime its gives NaT, There seems to be no time in the column only a number that shows year, mont and day as a large number.
Ellen
Peter Perkins
Peter Perkins on 10 Nov 2023
"I cant manage to convert this tot three columns containing Year, month , day"
Hard to say without context, but you may nt want to do that. Once you have a datetime (as Les shows), likely you can do what you need to without separate date components.

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 Accepted Answer

Les Beckham
Les Beckham on 7 Nov 2023
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2 votes

Ran in:
As @Stephen23 said, it is better to keep the date and time as a datetime array.
See below.
opts = delimitedTextImportOptions;
opts.DataLines = 34;
opts.VariableNames = {'STN', 'YYYYMMDD', 'HH', 'DD', 'FH', 'FF', 'FX', 'T', 'T10N', 'TD', 'SQ', 'Q', 'DR', 'RH', 'P', 'VV', 'N', 'U', 'WW', 'IX', 'M', 'R', 'S', 'O', 'Y'};
opts.VariableTypes = {'double', 'char', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double'};
% numel({'double', 'datetime', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double', 'double'})
T = readtable('uurgeg_310_2021-2030.txt', opts)
T = 24264×25 table
STN YYYYMMDD HH DD FH FF FX T T10N TD SQ Q DR RH P VV N U WW IX M R S O Y ___ ____________ __ ___ __ __ ___ __ ____ __ __ __ __ __ _____ __ _ __ ___ __ _ _ _ _ _ 310 {'20210101'} 1 300 30 40 60 35 NaN 18 0 0 0 0 10067 70 7 88 NaN 5 0 0 0 0 0 310 {'20210101'} 2 180 30 40 60 36 NaN 20 0 0 6 9 10072 70 8 89 23 7 0 1 0 0 0 310 {'20210101'} 3 220 30 30 50 30 NaN 18 0 0 3 6 10075 65 7 91 23 7 0 1 0 0 0 310 {'20210101'} 4 220 40 40 50 31 NaN 19 0 0 0 0 10074 65 7 91 NaN 5 0 0 0 0 0 310 {'20210101'} 5 300 20 10 50 37 NaN 26 0 0 4 1 10075 60 8 92 81 7 0 1 0 0 0 310 {'20210101'} 6 190 20 30 40 40 11 24 0 0 0 -1 10077 68 8 89 23 7 0 1 0 0 0 310 {'20210101'} 7 310 20 30 40 46 NaN 22 0 0 0 -1 10081 69 8 84 51 7 0 1 0 0 0 310 {'20210101'} 8 300 30 30 60 42 NaN 12 0 0 0 -1 10085 75 8 80 22 7 0 1 0 0 0 310 {'20210101'} 9 280 40 50 70 51 NaN 16 3 11 0 0 10089 75 8 77 2 7 0 0 0 0 0 310 {'20210101'} 10 280 50 50 70 54 NaN 18 3 31 0 0 10093 75 8 77 NaN 5 0 0 0 0 0 310 {'20210101'} 11 270 50 50 70 59 NaN 24 3 50 0 0 10095 67 8 78 NaN 5 0 0 0 0 0 310 {'20210101'} 12 270 50 60 80 62 27 22 7 81 0 0 10092 69 8 75 2 7 0 0 0 0 0 310 {'20210101'} 13 260 60 70 80 58 NaN 20 5 62 0 0 10092 72 8 76 NaN 5 0 0 0 0 0 310 {'20210101'} 14 260 70 70 90 56 NaN 19 0 21 0 0 10092 75 8 77 NaN 5 0 0 0 0 0 310 {'20210101'} 15 260 80 90 100 55 NaN 23 7 20 0 0 10094 69 8 79 NaN 5 0 0 0 0 0 310 {'20210101'} 16 250 80 90 100 54 NaN 23 2 6 0 0 10099 72 8 80 NaN 5 0 0 0 0 0
DateTime = table(datetime(T.YYYYMMDD, 'InputFormat', 'yyyyMMdd') + hours(T.HH));
T = [DateTime T];
T = renamevars(T, 'Var1', 'DateTime')
T = 24264×26 table
DateTime STN YYYYMMDD HH DD FH FF FX T T10N TD SQ Q DR RH P VV N U WW IX M R S O Y ____________________ ___ ____________ __ ___ __ __ ___ __ ____ __ __ __ __ __ _____ __ _ __ ___ __ _ _ _ _ _ 01-Jan-2021 01:00:00 310 {'20210101'} 1 300 30 40 60 35 NaN 18 0 0 0 0 10067 70 7 88 NaN 5 0 0 0 0 0 01-Jan-2021 02:00:00 310 {'20210101'} 2 180 30 40 60 36 NaN 20 0 0 6 9 10072 70 8 89 23 7 0 1 0 0 0 01-Jan-2021 03:00:00 310 {'20210101'} 3 220 30 30 50 30 NaN 18 0 0 3 6 10075 65 7 91 23 7 0 1 0 0 0 01-Jan-2021 04:00:00 310 {'20210101'} 4 220 40 40 50 31 NaN 19 0 0 0 0 10074 65 7 91 NaN 5 0 0 0 0 0 01-Jan-2021 05:00:00 310 {'20210101'} 5 300 20 10 50 37 NaN 26 0 0 4 1 10075 60 8 92 81 7 0 1 0 0 0 01-Jan-2021 06:00:00 310 {'20210101'} 6 190 20 30 40 40 11 24 0 0 0 -1 10077 68 8 89 23 7 0 1 0 0 0 01-Jan-2021 07:00:00 310 {'20210101'} 7 310 20 30 40 46 NaN 22 0 0 0 -1 10081 69 8 84 51 7 0 1 0 0 0 01-Jan-2021 08:00:00 310 {'20210101'} 8 300 30 30 60 42 NaN 12 0 0 0 -1 10085 75 8 80 22 7 0 1 0 0 0 01-Jan-2021 09:00:00 310 {'20210101'} 9 280 40 50 70 51 NaN 16 3 11 0 0 10089 75 8 77 2 7 0 0 0 0 0 01-Jan-2021 10:00:00 310 {'20210101'} 10 280 50 50 70 54 NaN 18 3 31 0 0 10093 75 8 77 NaN 5 0 0 0 0 0 01-Jan-2021 11:00:00 310 {'20210101'} 11 270 50 50 70 59 NaN 24 3 50 0 0 10095 67 8 78 NaN 5 0 0 0 0 0 01-Jan-2021 12:00:00 310 {'20210101'} 12 270 50 60 80 62 27 22 7 81 0 0 10092 69 8 75 2 7 0 0 0 0 0 01-Jan-2021 13:00:00 310 {'20210101'} 13 260 60 70 80 58 NaN 20 5 62 0 0 10092 72 8 76 NaN 5 0 0 0 0 0 01-Jan-2021 14:00:00 310 {'20210101'} 14 260 70 70 90 56 NaN 19 0 21 0 0 10092 75 8 77 NaN 5 0 0 0 0 0 01-Jan-2021 15:00:00 310 {'20210101'} 15 260 80 90 100 55 NaN 23 7 20 0 0 10094 69 8 79 NaN 5 0 0 0 0 0 01-Jan-2021 16:00:00 310 {'20210101'} 16 250 80 90 100 54 NaN 23 2 6 0 0 10099 72 8 80 NaN 5 0 0 0 0 0

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Peter Perkins
Peter Perkins on 10 Nov 2023
Probably best to then create TT as
TT = timetable(T,RowTimes=DateTime)
(Also best to not name variable quite so similarly to classes.)

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More Answers (2)

Stephen23
Stephen23 on 7 Nov 2023
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2 votes

Ran in:
Rather than fiddling around with text or numerics, just import the 2nd column as DATETIME right from the start:
fnm = 'uurgeg_310_2021-2030.txt';
opt = detectImportOptions(fnm, 'Delimiter',',', 'Range',32, 'VariableNamingRule','preserve');
opt = setvartype(opt, 'YYYYMMDD','datetime');
opt = setvaropts(opt, 'YYYYMMDD','InputFormat','uuuuMMdd');
tbl = readtable(fnm,opt)
tbl = 24264×25 table
# STN YYYYMMDD HH DD FH FF FX T T10N TD SQ Q DR RH P VV N U WW IX M R S O Y _____ ___________ __ ___ __ __ ___ __ ____ __ __ __ __ __ _____ __ _ __ ___ __ _ _ _ _ _ 310 01-Jan-2021 1 300 30 40 60 35 NaN 18 0 0 0 0 10067 70 7 88 NaN 5 0 0 0 0 0 310 01-Jan-2021 2 180 30 40 60 36 NaN 20 0 0 6 9 10072 70 8 89 23 7 0 1 0 0 0 310 01-Jan-2021 3 220 30 30 50 30 NaN 18 0 0 3 6 10075 65 7 91 23 7 0 1 0 0 0 310 01-Jan-2021 4 220 40 40 50 31 NaN 19 0 0 0 0 10074 65 7 91 NaN 5 0 0 0 0 0 310 01-Jan-2021 5 300 20 10 50 37 NaN 26 0 0 4 1 10075 60 8 92 81 7 0 1 0 0 0 310 01-Jan-2021 6 190 20 30 40 40 11 24 0 0 0 -1 10077 68 8 89 23 7 0 1 0 0 0 310 01-Jan-2021 7 310 20 30 40 46 NaN 22 0 0 0 -1 10081 69 8 84 51 7 0 1 0 0 0 310 01-Jan-2021 8 300 30 30 60 42 NaN 12 0 0 0 -1 10085 75 8 80 22 7 0 1 0 0 0 310 01-Jan-2021 9 280 40 50 70 51 NaN 16 3 11 0 0 10089 75 8 77 2 7 0 0 0 0 0 310 01-Jan-2021 10 280 50 50 70 54 NaN 18 3 31 0 0 10093 75 8 77 NaN 5 0 0 0 0 0 310 01-Jan-2021 11 270 50 50 70 59 NaN 24 3 50 0 0 10095 67 8 78 NaN 5 0 0 0 0 0 310 01-Jan-2021 12 270 50 60 80 62 27 22 7 81 0 0 10092 69 8 75 2 7 0 0 0 0 0 310 01-Jan-2021 13 260 60 70 80 58 NaN 20 5 62 0 0 10092 72 8 76 NaN 5 0 0 0 0 0 310 01-Jan-2021 14 260 70 70 90 56 NaN 19 0 21 0 0 10092 75 8 77 NaN 5 0 0 0 0 0 310 01-Jan-2021 15 260 80 90 100 55 NaN 23 7 20 0 0 10094 69 8 79 NaN 5 0 0 0 0 0 310 01-Jan-2021 16 250 80 90 100 54 NaN 23 2 6 0 0 10099 72 8 80 NaN 5 0 0 0 0 0
"I cant manage to convert this tot three columns containing Year, month , day"
[tbl.Year,tbl.Month,tbl.Day] = ymd(tbl.YYYYMMDD);
tbl % scroll to the right
tbl = 24264×28 table
# STN YYYYMMDD HH DD FH FF FX T T10N TD SQ Q DR RH P VV N U WW IX M R S O Y Year Month Day _____ ___________ __ ___ __ __ ___ __ ____ __ __ __ __ __ _____ __ _ __ ___ __ _ _ _ _ _ ____ _____ ___ 310 01-Jan-2021 1 300 30 40 60 35 NaN 18 0 0 0 0 10067 70 7 88 NaN 5 0 0 0 0 0 2021 1 1 310 01-Jan-2021 2 180 30 40 60 36 NaN 20 0 0 6 9 10072 70 8 89 23 7 0 1 0 0 0 2021 1 1 310 01-Jan-2021 3 220 30 30 50 30 NaN 18 0 0 3 6 10075 65 7 91 23 7 0 1 0 0 0 2021 1 1 310 01-Jan-2021 4 220 40 40 50 31 NaN 19 0 0 0 0 10074 65 7 91 NaN 5 0 0 0 0 0 2021 1 1 310 01-Jan-2021 5 300 20 10 50 37 NaN 26 0 0 4 1 10075 60 8 92 81 7 0 1 0 0 0 2021 1 1 310 01-Jan-2021 6 190 20 30 40 40 11 24 0 0 0 -1 10077 68 8 89 23 7 0 1 0 0 0 2021 1 1 310 01-Jan-2021 7 310 20 30 40 46 NaN 22 0 0 0 -1 10081 69 8 84 51 7 0 1 0 0 0 2021 1 1 310 01-Jan-2021 8 300 30 30 60 42 NaN 12 0 0 0 -1 10085 75 8 80 22 7 0 1 0 0 0 2021 1 1 310 01-Jan-2021 9 280 40 50 70 51 NaN 16 3 11 0 0 10089 75 8 77 2 7 0 0 0 0 0 2021 1 1 310 01-Jan-2021 10 280 50 50 70 54 NaN 18 3 31 0 0 10093 75 8 77 NaN 5 0 0 0 0 0 2021 1 1 310 01-Jan-2021 11 270 50 50 70 59 NaN 24 3 50 0 0 10095 67 8 78 NaN 5 0 0 0 0 0 2021 1 1 310 01-Jan-2021 12 270 50 60 80 62 27 22 7 81 0 0 10092 69 8 75 2 7 0 0 0 0 0 2021 1 1 310 01-Jan-2021 13 260 60 70 80 58 NaN 20 5 62 0 0 10092 72 8 76 NaN 5 0 0 0 0 0 2021 1 1 310 01-Jan-2021 14 260 70 70 90 56 NaN 19 0 21 0 0 10092 75 8 77 NaN 5 0 0 0 0 0 2021 1 1 310 01-Jan-2021 15 260 80 90 100 55 NaN 23 7 20 0 0 10094 69 8 79 NaN 5 0 0 0 0 0 2021 1 1 310 01-Jan-2021 16 250 80 90 100 54 NaN 23 2 6 0 0 10099 72 8 80 NaN 5 0 0 0 0 0 2021 1 1

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Ellen
Ellen on 9 Nov 2023
thx for learning me something new!
Ellen

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Peter Perkins
Peter Perkins on 10 Nov 2023
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1 vote

Ran in:
Worth saying that if the file was a spreadsheet and contained things like 20230101 as numeric values, there's a conversion for that too:
datetime(20230102,ConvertFrom="yyyymmdd")
ans = datetime
02-Jan-2023

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Asked:

Ellen
Ellen
on 7 Nov 2023

Answered:

Peter Perkins
Peter Perkins
on 10 Nov 2023

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