Create Strings

We can use the following ways to create a string:

(1) Use single quotes (‘), double quotes (“), or back quotes (`).

A few things to notice:

  • Back quotes are very convenient, but they cannot be used for strings that contain spaces or symbols.

  • To create a string with only one character, we can use back quotes or double quotes but not single quotes. Single quotes around one character create a CHAR instead of STRING.

$ var1='DolphinDB version 1.1';
$ var2="This is DolphinDB";
$ var3=`DolphinDB;
$ var4=['IBM', 'MSFT', 'GOOG', 'FB'];
$ var5=["IBM","MSFT","GOOG","FB"];
$ var6=`IBM`MSFT`GOOG`FB;
$ typestr(`C);
STRING

$ typestr("C");
STRING

$ typestr('C');
CHAR

(2) Use function string.

$ var7=string(108.5);

(3) Use function format. It applies a specified format to the given object to produce a string scalar/vector. Depending on the data type of the input, function format calls either function decimalFormat or temporalFormat.

$ t = table(1..100 as id, (1..100 + 2018.01.01) as date, rand(100.0, 100) as price, rand(10000, 100) as qty);
$ t;

id

date

price

qty

1

2018.01.02

70.832104

1719

2

2018.01.03

12.22557

6229

3

2018.01.04

8.695886

1656

4

2018.01.05

24.324535

2860

5

2018.01.06

0.443173

6874

6

2018.01.07

90.302176

3277

7

2018.01.08

78.556843

3424

8

2018.01.09

45.836447

8636

9

2018.01.10

57.416425

707

10

2018.01.11

98.879764

2267

…

…

…

…

 
$ t1=select id, date.format("MM/dd/yyyy") as date, price.format("00.00") as price, qty.format("#,###") as qty from t;
$ t1;

id

date

price

qty

1

01/02/2018

70.83

1,719

2

01/03/2018

12.23

6,229

3

01/04/2018

08.70

1,656

4

01/05/2018

24.32

2,860

5

01/06/2018

00.44

6,874

6

01/07/2018

90.30

3,277

7

01/08/2018

78.56

3,424

8

01/09/2018

45.84

8,636

9

01/10/2018

57.42

707

10

01/11/2018

98.88

2,267

…

…

…

…

 
$ t1.date.typestr();
STRING VECTOR

The following table shows the symbols used in the parameter format of function decimalFormat. Please check the section Parsing and Format of Temporal Variables regarding the parameter format of function temporalFormat.

Symbol

Meaning

Notes

0

mandatory digit

note 1

#

optional digit

note 2

.

decimal point

%

percent sign

note 3

E

separates mantissa and exponent in scientific notation.

note 4

,

grouping separator

note 5

;

separates the format for positive numbers and the format for negative numbers

note 6

  • Note 1: The number of 0s before the decimal point means the minimum number of digits before the decimal point. In comparison, the number of 0s after the decimal point means the number of digits after the decimal point.

$ decimalFormat(123,"0");
123

$ decimalFormat(123,"00000");
00123

$ decimalFormat(123.45,"0");
123

$ decimalFormat(123.45,"0.0");
123.5

$ decimalFormat(123.45,"0.000");
123.450

$ decimalFormat(123.45, ".0");
123.5

$ decimalFormat(0.45, ".0");
.5

  • Note 2: If 0s and #s are used together after the decimal point, 0s must appear before #s.

$ decimalFormat(123.45,"0.#");
123.5

$ decimalFormat(123.45,"0.###");
123.45

$ decimalFormat(123.456,"0.000###");
123.456

$ decimalFormat(123.456789110,"0.000###");
123.456789

$ decimalFormat(0.345, ".##");
.35

  • Note 3: % is always at the end of a format. % and E cannot both appear in a format.

$ decimalFormat(0.125,"0.00%");
12.50%

$ decimalFormat(0.125, "#.##%");
12.5%

$ decimalFormat(0.12567,"#.##%");
12.57%

  • Note 4: “E” is followed by at least one 0 and 0s only.

$ decimalFormat(1234567.89,"0.##E00");
1.23E06

$ decimalFormat(0.0000000000123456789,"0.000E0");
1.235E-11

  • Note 5: The grouping separator may only appear at most once in the parameter format. The number of digits between the grouping separator and the decimal point (if the decimal point is used) or the end of the format (if the decimal point is not used) determines the number of digits between grouping separators in the result.

$ decimalFormat(123456789,"#,###");
123,456,789

$ decimalFormat(123456789.166,"#,###.##");
123,456,789.17

$ decimalFormat(123456789.166,"0,000.00");
123,456,789.17

  • Note 6: If we prefer to apply different formats to an object depending on whether it is positive or negative, we can use “;” to seperate the 2 formats.

$ decimalFormat(123.456,"0.00#E00;(0.00#E00)");
1.235E02

$ decimalFormat(-123.456,"0.00#E00;(0.00#E00)");
(1.235E02)

(4) Use the escape character.

Use of the escape character

Meaning

\n

new line

\r

carriage return

\t

tab

\

backslash

\’

single quote

\”

double quote

 
$ x="ABC\\DEF";
$ x;
ABC\DEF

$ x="ABC\"D\'EF";
$ x;
ABC"D'EF

If a string only contains one type of quotes (single quotes or double quotes), the simplest way to create it is to use the other type of quotes.

$ x="ABC'D'EF";
$ x;
ABC'D'EF

$ x='ABC"DEF';
4 x;
ABC"DEF