mf_substr.hlp

是一个经济学管理应用软件 很难找的 但是经济学学生又必须用到

{smcl}
{* 28mar2005}{...}
{cmd:help mata substr()}
{hline}
{* index substr()}{...}

{title:Title}

{p 4 4 2}
{bf:[M-5] substr() -- Extract substring}


{title:Syntax}

{p 8 12 2}
{it:string matrix}
{cmd:substr(}{it:string matrix s}{cmd:,}
{it:real matrix b}{cmd:,}
{it:real matrix l}{cmd:)}

{p 8 12 2}
{it:string matrix}
{cmd:substr(}{it:string matrix s}{cmd:,}
{it:real matrix b}{cmd:)}


{title:Description}

{p 4 4 2}
{cmd:substr(}{it:s}{cmd:,} {it:b}{cmd:,} {it:l}{cmd:)}
returns the substring of {it:s} starting at position {it:b} and 
continuing for a length of {it:l}, where

{p 8 12 2}
1.  {it:b} specifies the starting position; 
    the first character of the string is {it:b}=1.

{p 8 12 2}
2.  {it:b}>0 is interpreted as distance from the start of the string; 
    {it:b}=2 means starting at the second character.

{p 8 12 2}
3.  {it:b}<0 is interpreted as distance from end of string; {it:b} = -1 means
    starting at the last character; 
    {it:b} = -2 means starting at the second from the last character.

{p 8 12 2}
4.  {it:l} specifies the length; {it:l}=2 means for two characters.

{p 8 12 2}
5.  {it:l}<0 is treated the same as {it:l}=0:  no characters are copied.

{p 8 12 2}
6.  {it:l}>={cmd:.} is interpreted to mean to the end of the string.

{p 4 4 2}
{cmd:substr(}{it:s}{cmd:,} {it:b}{cmd:)}
is equivalent to 
{cmd:substr(}{it:s}{cmd:,} {it:b}{cmd:,} {cmd:.)}
for strings that do not contain binary 0.  If there is a binary 0 to
the right of {it:b}, the substring from {it:b} up to but not including the
binary 0 is returned.

{p 4 4 2}
When arguments are not scalar, {cmd:substr()} returns element-by-element
results.


{title:Conformability}

    {cmd:substr(}{it:s}{cmd:,} {it:b}{cmd:,} {it:l}{cmd:)}:
	{it:s}:  {it:r1 x c1}
	{it:b}:  {it:r2 x c2}
	{it:l}:  {it:r3 x c3}; {it:s}, {it:b}, and {it:l} r-conformable
   {it:result}:  max({it:r1},{it:r2},{it:r3}) {it:x} max({it:c1},{it:c2},{it:c3})

    {cmd:substr(}{it:s}{cmd:,} {it:b}{cmd:)}:
	{it:s}:  {it:r1 x c1}
	{it:b}:  {it:r2 x c2}; {it:s} and {it:b} r-conformable
   {it:result}:  max({it:r1},{it:r2}) {it:x} max({it:c1},{it:c2})


{title:Diagnostics}

{p 4 4 2}
In 
{cmd:substr(}{it:s}{cmd:,} {it:b}{cmd:,} {it:l}{cmd:)}
and 
{cmd:substr(}{it:s}{cmd:,} {it:b}{cmd:)}, 
if {it:b} describes a position before the beginning of the string or 
after the end, "" is returned.
If {it:b}+{it:l} describes a position to the right of the end of the 
string, results are as if a smaller value for {it:l} were specified.


{title:Source code}

{p 4 4 2}
Function is built-in.


{title:Also see}

{p 4 13 2}
Manual:  {hi:[M-5] substr()}

{p 4 13 2}
Online:  help for 
{bf:{help m4_string:[M-4] string}}
{p_end}