www.gusucode.com > datastoreio工具箱 matlab源码程序 > datastoreio/+matlab/+io/+datastore/@KeyValueDatastore/preview.m
function data = preview(kvds) %PREVIEW Read key-value pairs from the start of a KeyValueDatastore. % T = PREVIEW(KVDS) reads key-value pairs from the beginning of KVDS. % T is a table with variables 'Key' and 'Value'. % KVDS.ReadSize controls the number of key-value pairs that are read. % PREVIEW does not affect the state of KVDS. % % Example: % -------- % % 'mapredout.mat' is the output file of a mapreduce function. % kvds = datastore('mapredout.mat') % kvds.ReadSize = 3 % % PREVIEW 3 key-value pairs % kv3 = PREVIEW(kvds) % % See also matlab.io.datastore.KeyValueDatastore, hasdata, readall, read, reset. % Copyright 2014-2016 The MathWorks, Inc. try % If files are empty, use READALL to get the correct empty table if isEmptyFiles(kvds) data = readall(kvds); return; end kvdsCopy = copy(kvds); reset(kvdsCopy); warning('off', 'MATLAB:MatFile:OlderFormat'); c = onCleanup(@() warning('on', 'MATLAB:MatFile:OlderFormat')); data = read(kvdsCopy); catch e throw(e); end end