Esempio: manipolazione delle variabili di stringa

Funzioni > Funzioni di utilità > Esempio: manipolazione delle variabili di stringa

Utilizzare concatenazione, stringhe secondarie e altre modifiche elementari delle stringhe di caratteri.

Stringhe per i nomi di file

1. Definire le stringhe di caratteri di input a e b.

2. Utilizzare la funzione concat con la variabile della directory di lavoro corrente (CWD) per creare nomi di percorso per le funzioni di lettura dei file.

Questo nome di variabile può essere passato alla funzione READFILE, ad esempio, o a un ciclo di programma per leggere in sequenza i file di una directory.

È inoltre possibile utilizzare la funzione format per concatenare stringhe combinate con variabili.

Stringhe secondarie e posizione

1. Utilizzare la funzione substr per estrarre la stringa che inizia alla posizione 3 e contiene quattro caratteri.

2. Utilizzare la funzione strlen per calcolare la lunghezza della stringa c.

3. Utilizzare la funzione search per individuare la posizione iniziale della stringa secondaria dell'estensione del file in c.

4. Scrivere un programma per trovare tutte le occorrenze di una stringa secondaria in una stringa di caratteri.

Fare clic per copiare questa espressione

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              <apply>
                <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">search</id>
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                <real>1</real>
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5. Utilizzare il programma per trovare tutte le occorrenze di "in" nella stringa seguente.

Conversione di stringhe in numeri

1. Utilizzare le funzioni rows, cols, IsString, search, concat, substr, strlen e str2num per convertire stringhe in numeri.

Le matrici possono contenere combinazioni di stringhe e numeri. Le funzioni di ricerca possono essere utilizzate per cercare sia stringhe che numeri.

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                                <id labels="FUNCTION" xml:space="preserve">search</id>
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                                    <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
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                                      <id xml:space="preserve">i</id>
                                      <id xml:space="preserve">j</id>
                                    </sequence>
                                  </apply>
                                  <str xml:space="preserve">,</str>
                                  <real>0</real>
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                          <real>-1</real>
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                              <id labels="VARIABLE" xml:space="preserve">m</id>
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                                <id labels="*" xml:space="preserve">j</id>
                              </sequence>
                            </apply>
                            <apply>
                              <id labels="FUNCTION" xml:space="preserve">concat</id>
                              <sequence>
                                <apply>
                                  <id labels="FUNCTION" xml:space="preserve">substr</id>
                                  <sequence>
                                    <apply>
                                      <indexer />
                                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                                      <sequence>
                                        <id xml:space="preserve">i</id>
                                        <id xml:space="preserve">j</id>
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                                    <real>0</real>
                                    <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">k</id>
                                  </sequence>
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                                <str xml:space="preserve">.</str>
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                                  <sequence>
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                                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                                      <sequence>
                                        <id xml:space="preserve">i</id>
                                        <id xml:space="preserve">j</id>
                                      </sequence>
                                    </apply>
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                                      <plus />
                                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">k</id>
                                      <real>1</real>
                                    </apply>
                                    <apply>
                                      <id labels="FUNCTION" xml:space="preserve">strlen</id>
                                      <apply>
                                        <indexer />
                                        <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                                        <sequence>
                                          <id xml:space="preserve">i</id>
                                          <id xml:space="preserve">j</id>
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                            <id labels="*" xml:space="preserve">j</id>
                          </sequence>
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                        <apply>
                          <id labels="FUNCTION" xml:space="preserve">str2num</id>
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                            <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
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                              <id xml:space="preserve">j</id>
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        <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
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2. Utilizzare il programma per convertire in numeri le stringhe contenute nella matrice M.

Questo programma utilizza str2num per convertire stringhe in numeri. Per convertire numeri in stringhe, utilizzare num2str.

3. Modificare il programma in modo che restituisca un messaggio di errore se la matrice contiene elementi che non sono stringhe e quindi utilizzarlo.

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                                <id labels="FUNCTION" xml:space="preserve">search</id>
                                <sequence>
                                  <apply>
                                    <indexer />
                                    <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                                    <sequence>
                                      <id xml:space="preserve">i</id>
                                      <id xml:space="preserve">j</id>
                                    </sequence>
                                  </apply>
                                  <str xml:space="preserve">,</str>
                                  <real>0</real>
                                </sequence>
                              </apply>
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                          </parens>
                          <real>-1</real>
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                              <id labels="VARIABLE" xml:space="preserve">m</id>
                              <sequence>
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                                <id labels="*" xml:space="preserve">j</id>
                              </sequence>
                            </apply>
                            <apply>
                              <id labels="FUNCTION" xml:space="preserve">concat</id>
                              <sequence>
                                <apply>
                                  <id labels="FUNCTION" xml:space="preserve">substr</id>
                                  <sequence>
                                    <apply>
                                      <indexer />
                                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                                      <sequence>
                                        <id xml:space="preserve">i</id>
                                        <id xml:space="preserve">j</id>
                                      </sequence>
                                    </apply>
                                    <real>0</real>
                                    <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">k</id>
                                  </sequence>
                                </apply>
                                <str xml:space="preserve">.</str>
                                <apply>
                                  <id labels="FUNCTION" xml:space="preserve">substr</id>
                                  <sequence>
                                    <apply>
                                      <indexer />
                                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                                      <sequence>
                                        <id xml:space="preserve">i</id>
                                        <id xml:space="preserve">j</id>
                                      </sequence>
                                    </apply>
                                    <apply>
                                      <plus />
                                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">k</id>
                                      <real>1</real>
                                    </apply>
                                    <apply>
                                      <id labels="FUNCTION" xml:space="preserve">strlen</id>
                                      <apply>
                                        <indexer />
                                        <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                                        <sequence>
                                          <id xml:space="preserve">i</id>
                                          <id xml:space="preserve">j</id>
                                        </sequence>
                                      </apply>
                                    </apply>
                                  </sequence>
                                </apply>
                              </sequence>
                            </apply>
                          </localDefine>
                        </program>
                      </while>
                      <localDefine>
                        <apply>
                          <indexer />
                          <id labels="VARIABLE" xml:space="preserve">m</id>
                          <sequence>
                            <id labels="*" xml:space="preserve">i</id>
                            <id labels="*" xml:space="preserve">j</id>
                          </sequence>
                        </apply>
                        <apply>
                          <id labels="FUNCTION" xml:space="preserve">str2num</id>
                          <apply>
                            <indexer />
                            <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                            <sequence>
                              <id xml:space="preserve">i</id>
                              <id xml:space="preserve">j</id>
                            </sequence>
                          </apply>
                        </apply>
                      </localDefine>
                    </program>
                  </then>
                  <else>
                    <program>
                      <apply>
                        <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">error</id>
                        <str xml:space="preserve">This is not a string!</str>
                      </apply>
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                  </else>
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            </for>
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        <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
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Nella seconda chiamata le funzioni hanno restituito il messaggio di errore specificato come parametro della funzione error.

4. Scrivere un programma per creare un vettore da una stringa di caratteri costituita da una sequenza numerica. Ogni numero è separato dal precedente tramite una virgola (,) e uno spazio.

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                  <id xml:space="preserve">j</id>
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                <real>1</real>
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              <id labels="VARIABLE" xml:space="preserve">j</id>
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              <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">v</id>
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              <real>-1</real>
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                <id labels="VARIABLE" xml:space="preserve">V</id>
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                  <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">str2num</id>
                  <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">S</id>
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                <id labels="VARIABLE" xml:space="preserve">i</id>
                <real>0</real>
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              <for>
                <id labels="*" xml:space="preserve">j</id>
                <range>
                  <real>0</real>
                  <apply>
                    <minus />
                    <apply>
                      <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">rows</id>
                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">v</id>
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                    <real>1</real>
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                      <indexer />
                      <id labels="VARIABLE" xml:space="preserve">V</id>
                      <id labels="*" xml:space="preserve">j</id>
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                    <apply>
                      <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">str2num</id>
                      <apply>
                        <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">substr</id>
                        <sequence>
                          <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">S</id>
                          <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">i</id>
                          <apply>
                            <minus />
                            <apply>
                              <indexer />
                              <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">v</id>
                              <id xml:space="preserve">j</id>
                            </apply>
                            <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">i</id>
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                        </sequence>
                      </apply>
                    </apply>
                  </localDefine>
                  <localDefine>
                    <id labels="VARIABLE" xml:space="preserve">i</id>
                    <apply>
                      <plus />
                      <apply>
                        <indexer />
                        <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">v</id>
                        <id xml:space="preserve">j</id>
                      </apply>
                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">m</id>
                    </apply>
                  </localDefine>
                </program>
              </for>
              <localDefine>
                <apply>
                  <indexer />
                  <id labels="VARIABLE" xml:space="preserve">V</id>
                  <apply>
                    <id labels="*" xml:space="preserve">rows</id>
                    <id labels="*" xml:space="preserve">v</id>
                  </apply>
                </apply>
                <apply>
                  <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">str2num</id>
                  <apply>
                    <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">substr</id>
                    <sequence>
                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">S</id>
                      <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">i</id>
                      <apply>
                        <minus />
                        <apply>
                          <id labels="FUNCTION" xml:space="preserve" label-is-contextual="true">strlen</id>
                          <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">S</id>
                        </apply>
                        <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">i</id>
                      </apply>
                    </sequence>
                  </apply>
                </apply>
              </localDefine>
            </program>
          </else>
        </if>
        <id labels="VARIABLE" xml:space="preserve" label-is-contextual="true">V</id>
      </program>
    </define>
  </math>
</region>

5. Utilizzare il programma per convertire in vettore la sequenza di caratteri seguente.

Conversioni di codici ASCII

1. Utilizzare la funzione str2vec per convertire una stringa in un vettore di codici ASCII.

2. Utilizzare la funzione vec2str per convertire un vettore di codici ASCII in una stringa.

3. Utilizzare le funzioni str2vec e vec2str per convertire stringhe di caratteri da lettere maiuscole a minuscole e viceversa.

a. Utilizzare la funzione str2vec per definire i caratteri maiuscoli o minuscoli.

b. Utilizzare le funzioni str2vec e vect2str per definire le variabili con caratteri maiuscoli o minuscoli.

c. Utilizzare le definizioni precedenti per convertire la stringa di caratteri S con caratteri minuscoli.

d. Utilizzare le definizioni precedenti per convertire la stringa di caratteri T con caratteri maiuscoli.

Argomenti correlati

Funzioni di stringa

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