MATLAB: Help using the arrayfun() function to apply strsplit() to all entries in a string array

Question

I'm trying to wrap my head around how the arrayfun() function works and would greatly appreciate some help with a specific example:

I have a string array of weather data.

weather_strings = 
  10×1 string array
    "UTC,2140991,49.0"
    "UTC,2140992,49.1"
    "UTC,2140993,49.1"
    ...

I need to extract the values after the second comma (temperatures) as a 1×10 matrix of doubles, [49.0, 49.1, 49.1, …].

I've figured out a clunky way to do this for a single entry (please let me know if there's a better way).

weather_string = weather_strings(1) % extract only the first entry
weather_string_split = strsplit(weather_string, ',') % apply strsplit() to split on commas
weather_string_split_trim = weather_string_split(:,3) % extract only 3rd column
weather_num_trim = str2num(weather_string_split_trim) % convert from string to double

But I can't seem to figure out how to use arrayfun() to apply that to every entry. I've tried:

weather_strings_split = arrayfun(strsplit(weather_strings,','), weather_strings) % apply stringsplit to split on commas, for all elements?

which gives the error message:

Error using strsplit (line 80)
First input must be either a character vector or a string scalar.
Error in test_window (line 17)
weather_strings_split = arrayfun(strsplit(weather_strings,','), weather_strings)

I'm probably missing something painfully obvious. What is it? I'm still somewhat of a beginner at coding, so I welcome you to explain it to me like I'm 5 years old.

Alternatively, if there's a clever way to extract these numbers directly from this data table (which came directly from a webread() function), I'd love to hear it. Var3 is a cell array.

weather_data_table =
  10×3 table
       Var1         Var2             Var3       
    __________    ________    __________________
    2018-11-26    17:41:25    'UTC,2140991,49.0'
    2018-11-26    17:42:27    'UTC,2140992,49.1'
    2018-11-26    17:43:28    'UTC,2140993,49.1'
...

Again, the goal is to get just the last numbers after the second comma of Var3 into a 1D matrix.

Thanks in advance!

Answer 1

Try this:

for k1 = 1:size(weather_strings,1)
    Col3(k1,:) = str2double(regexp(weather_strings{k1}, '\d*\.\d*', 'match'));
end
Col3 =
   49.0000
   49.1000
   49.1000

The loop is necessary because regexp is not vectorised. It can only handle one srting at a time.