How to extract string/numbers after a keyword in a text

Hi,

I have a text like the following.

z

>HEAD

DATAID="P=01 R=14 (H)"

ACQBY="DGSM"

FILEBY=""

ACQDATE=04/11/22

ENDDATE=04/13/22

FILEDATE=02/16/23

COUNTRY="UG"

LAT=3:26:1.6

LONG=30:56:25.9

ELEV=1224.44

UNITS=M

STDVERS="SEG 1.0"

PROGDATE="10/20/20"

EMPTY=1.0E32

>INFO MAXINFO=108

UNIQUE ID: {fd652be6-76e5-476d-ace0-bf2981887cf2}

PROCESS DATE: 2022-06-29 18:13

DURATION: 38 h 36 m 20 s

DECLINATION: 2°

...

...

How to extract the corresponding value after a given keyword? For instance, I would like to have

keyword = "LAT"

lat = [3,26,1.6];

keyword = "ACQDATE"

date = 04/11/22;

keyword = "EMPTY"

emptyval = 1.0E32;

keyword = "UNIQUE ID"

uid = 'fd652be6-76e5-476d-ace0-bf2981887cf2';

...

Would there be a function that can take care of all types of values?

Thanks,

Jasmine

[the cyclist]

Can you upload the text file? You can use the paper clip icon in the INSERT section of the toolbar.

Also, can you be more specific about what you need? For example, do you just want to input a keyword, and have MATLAB store/output the corresponding value? Or, do you want MATLAB to figure out all the keyword-value pairs and store them?

[Jasmine Zhu]

I would like to input the keyword, and get the corresponding value. The file was attached here.

Answer 1

[dpb]

"How to extract the corresponding value after a given keyword?"

data=readlines('Example.txt');  % bring the file into memory for efficiency -- don't open/close every time
keywords=extractBefore(data,"="); % split off keywords for matching -- same length vector as rows in data
instr='';
while ~matches(upper(instr),'Q')
  instr=input("Enter keyword wanted ('Q' to Quit)",'s');
  value=extractAfter(data(matches(keywords,instr)),"=");
  disp(value)
end

"Would there be a function that can take care of all types of values?"

Only a cell can hold any data type; as the above code snippet illustrates, return the data as a string first, then worry about converting it to the proper data type. But, there is no magic elixir potion there; you'll have to have a lookup table of the data type by keyword or do some parsing testing logic to try to automagically figure out what the variable types are.

datetime may not be too hard; they may be the only field with the forward slash or can use that the keyword may always contain the substring "DATE". I noticed one "DURATION"; study may show other patterns that can be taken advantage of other than just trying to convert. Strings appear to be delimited with " so that also is a clue.

ADDENDUM: Edited to use separate keywords array so can match explicitly without other gyrations. One could split the original array into two arrays with split on the "=" sign, but that would entail removing the other header records as split() is very unforgiving in requiring exactly the same number of fields for every record.

[Jasmine Zhu]

Not quite right. It worked once changed to data(contains(data,instr)). But thanks for letting me know the readlines() and extractAfter().

[dpb]

Was "air code" -- "contains" may be safe for this function, but it might be risky and, depending upon what the total population of keywords is, it might not always produce the desired result. If one keyword is a substring within another, both will match whereas you should ensure there is only one match.

The more robust solution would be to first extract the keywords as in

keywords=extractBefore(data,"=");

then do the matches comparison on that set instead of the full string.

[Jasmine Zhu]

Very helpful. Thank you!

Answer 2

[Image Analyst]

You might like to know about dictionary

help dictionary

 dictionary - Object that maps unique keys to values
    A dictionary is useful for fast lookup of values in a larger set.

    Creation
      Syntax
        d = dictionary(keys,values)
        d = dictionary(k1,v1,...,kN,vN)
        d = dictionary

      Input Arguments
        keys - Keys
          scalar | array
        values - Values
          scalar | array | cell array
        k1,v1,...,kN,vN - Key-value pairs (as separate arguments)
          scalar | array

    Usage
      Syntax
        valueOut = d(keys)
        d(keys) = newValues
        d(keys) = []
        valueOut = d{keys}
        d{keys} = newValues

    Object Functions
      entries      - Key-value pairs of dictionary
      isConfigured - Determine if dictionary has types assigned to keys and values
      isKey        - Determine if dictionary contains key
      keys         - Keys of dictionary
      numEntries   - Number of key-value pairs in dictionary
      types        - Types of dictionary keys and values
      values       - Values of dictionary

    Examples
      Create and Manage a Dictionary
      Store Multiple Data Types in a Dictionary
      Create Empty Configured Dictionary
      Add Entries to Unconfigured Dictionary

    See also entries, keys, values, types, numEntries, isConfigured, isKey,
      keyHash, keyMatch

    Introduced in MATLAB in R2022b
    Documentation for dictionary
       doc dictionary