loadText

loadText(filename, [delimiter], [schema], [skipRows=0], [arrayDelimiter], [containHeader], [arrayMarker])

filename is the input text file name with its absolute path. Currently only .csv files are supported.

delimiter (optional) is a STRING scalar indicating the table column separator. It can consist of one or more characters, with the default being a comma (',').

skipRows (optional) is an integer between 0 and 1024 indicating the rows in the beginning of the text file to be ignored. The default value is 0.

arrayDelimiter (optional) is a single character indicating the delimiter for columns holding the array vectors in the file. You must use the schema parameter to update the data type of the type column with the corresponding array vector data type before import.

containHeader (optional) is a Boolean value indicating whether the file contains a header row. The default value is NULL.

arrayMarker is a string containing 2 characters or a CHAR pair. These two characters represent the identifiers for the left and right boundaries of an array vector. The default identifiers are double quotes (").

• It cannot contain spaces, tabs (\t), or newline characters (\t or \n).

• It cannot contain digits or letters.

• If one is a double quote ("), the other must also be a double quote.

• If the identifier is ', ", or \, a backslash ( \ ) escape character should be used as appropriate. For example, arrayMarker="\"\"".

• If delimiter specifies a single character, arrayMarker cannot contain the same character.

• If delimiter specifies multiple characters, the left boundary of arrayMarker cannot be the same as the first character of delimiter.

Load a text file into memory as a table. loadText loads data in single thread. To load data in multiple threads, use ploadText .

• How a header row is determined:

  • The first row of the file is read in string format, and the column names are parsed from that data. Please note that the upper limit for the first row is 256 KB. If none of the columns in the first row of the file starts with a number, the first row is treated as the header with column names of the text file. If at least one of the columns in the first row of the file starts with a number, the system uses col0, col1, … as the column names;

  • When containHeader is true, the first row is determined as the header row, and the column names are parsed from that data;

  • When containHeader is false, the system uses col0, col1, … as the column names.

• How the column types are determined:

  • When loading a text file, the system determines the data type of each column based on a random sample of rows. This convenient feature may not always accurately determine the data type of all columns. We recommend users check the data type of each column with the extractTextSchema function after loading.
  • When the input file contains dates and times:
    • For data with delimiters (date delimiters "-", "/" and ".", and time delimiter ":"), it will be converted to the corresponding type. For example, "12:34:56" is converted to the SECOND type; "23.04.10" is converted to the DATE type.
    • For data without delimiters, data in the format of "yyMMdd" that meets 0<=yy<=99, 0<=MM<=12, 1<=dd<=31, will be preferentially parsed as DATE; data in the format of "yyyyMMdd" that meets 1900<=yyyy<=2100, 0<=MM<=12, 1<=dd<=31 will be preferentially parsed as DATE.
  • If a column does not have the expected data type, then we need to enter the correct data type of the column in the schema table. Users can also specify data types for all columns. For a temporal column, if it does not have the expected data type, we also need to specify a format such as "MM/dd/yyyy" in the schema table. For details about temporal formats please refer to Parsing and Format of Temporal Variables.

To load a subset of columns, specify the column index in the "col" column of schema.

As string in DolphinDB is encoded in UTF-8, we require input text files be encoded in UTF-8.

A few examples:

Use the following script to generate the data file to be used for the examples:

n=10
sym=rand(`AAPL`ORCL`MS`SUN,n)
permno=take(10001,n)
date=rand(2019.06.01..2019.06.10,n)
open=rand(100.0,n)
high=rand(200.0,n)
close=rand(200.0,n)
pre_close=rand(200.0,n)
change=rand(100.0,n)
vol=rand(10000,n)
amount=rand(100000.0,n)
t=table(sym,permno,date,open,high,close,pre_close,change,vol,amount)
saveText(t,"C:/DolphinDB/Data/stock.csv");

Example: Use loadText without specifying any optional parameters:

tt=loadText("C:/DolphinDB/Data/stock.csv");
tt;

schema(tt).colDefs;

Example: Specify the data type of a column before loading the file.

We may want to change the data type of column "permno" to be SYMBOL. For this, we need to use function extractTextSchema to get the schema table, update it, then load the text file with the revised schema table.

schema=extractTextSchema("C:/DolphinDB/Data/stock.csv");
update schema set type=`SYMBOL where name=`permno;
tt=loadText("C:/DolphinDB/Data/stock.csv",,schema);
schema(tt).colDefs;

You can also specify the data types of all columns:

schematable=table(`sym`permno`date`open`high`close`pre_close`change`vol`amount as name,`SYMBOL`SYMBOL`DATE`DOUBLE`DOUBLE`DOUBLE`DOUBLE`DOUBLE`INT`DOUBLE as type)
tt=loadText("C:/DolphinDB/Data/stock.csv",,schematable)
schema(tt).colDefs;

Example: Load only a subset of columns.

For example, we may only need to load the following 7 columns: sym, date, open, high, close, vol, amount. Please note that we cannot change the order of columns when loading data. To change the order of columns in the loaded table, use function reorderColumns!.

schema=extractTextSchema("C:/DolphinDB/Data/stock.csv");
schema=select * from schema where name in `sym`date`open`high`close`vol`amount
schema[`col]=[0,2,3,4,5,8,9]

tt=loadText("C:/DolphinDB/Data/stock.csv",,schema);
tt;

Example: Skip the first 2 rows when loading.

Please note that as the header is the first line of the text file, it is also skipped.

re=loadText(filename="C:/DolphinDB/Data/stock.csv",skipRows=2)
select count(*) from re;

Example: Specify the temporal format when loading the file.

Generate the text file to be used:

time=["20190623145457","20190623155423","20190623163025"]
sym=`AAPL`MS`IBM
qty=2200 5400 8670
price=54.78 59.64 65.23
t=table(time,sym,qty,price)
saveText(t,"C:/DolphinDB/Data/t2.csv");

Obtain the text schema with extractTextSchema before loading the file:

extractTextSchema("C:/DolphinDB/Data/t2.csv");

From the example above, if we load this text file without specifying the format of column "time", column "time" is empty as the system cannot parse the raw data correctly. For this scenario we must specify the format of the column.

schema=extractTextSchema("C:/DolphinDB/Data/t2.csv")
update schema set type = "DATETIME" where name = "time"
schema[`format]=["yyyyMMddHHmmss",,,];

loadText("C:/DolphinDB/Data/t2.csv",,schema);

Example: Load array vectors

bid = array(DOUBLE[], 0, 20).append!([1.4799 1.479 1.4787, 1.4796 1.479 1.4784, 1.4791 1.479 1.4784])
ask = array(DOUBLE[], 0, 20).append!([1.4821 1.4825 1.4828, 1.4818 1.482 1.4821, 1.4814 1.4818 1.482])
TradeDate = 2022.01.01 + 1..3
SecurityID = rand(`APPL`AMZN`IBM, 3)
t = table(SecurityID as `sid, TradeDate as `date, bid as `bid, ask as `ask)
t;
saveText(t,filename="/home/t.csv",delimiter=',',append=true)

path = "/home/t.csv"
schema=extractTextSchema(path);
update schema set type = "DOUBLE[]" where name="bid" or name ="ask"
t = loadText(path, schema=schema, arrayDelimiter=",")
t;

sid,date,bid,ask
APPL,2022.01.02,"1.4799,1.479,1.4787","1.4821,1.4825,1.4828"
IBM,2022.01.03,"1.4796,1.479,1.4784","1.4818,1.482,1.4821"
APPL,2022.01.04,"1.4791,1.479,1.4784","1.4814,1.4818,1.482"

sid,date,bid,ask
APPL,2022.01.02,[1.4799,1.479,1.4787],[1.4821,1.4825,1.4828]
IBM,2022.01.03,[1.4796,1.479,1.4784],[1.4818,1.482,1.4821]
APPL,2022.01.04,[1.4791,1.479,1.4784],[1.4814,1.4818,1.482]

path = "/home/DolphinDB/Data/t.csv"
schema=extractTextSchema(path);
update schema set type = "DOUBLE[]" where name="bid" or name ="ask"
t = loadText(path, schema=schema, arrayDelimiter=",",arrayMarker="[]")
t;